I've built two huge shops myself, I know what you're going through. May I make some suggestions? What am I saying... I'mm gonna anyway, so here goes.
Go for the most square footage you can. Not only does it give you "more" than what you need (at the onset, at least) you'll always grow into it. It'll also add value to your property. Do it to code! Don't fall short and slap up a pole building that will only fall short of reliability, functionality, durability in all climate conditions, and equity value.
That said, keep this in mind, too... you can be your own general contractor and negotiate every aspect of your construction build yourself. Begin dreaming big (always). Draw yourself out the site plan layout of where the structure will sit on the property. Walk it time and time again to ensure it's the "ideal" location. Once that's settled, rent yourself a bobcat (150 bucks for two days/weekend effort), pick it up on a friday evening, drop it off sunday evening. DONE. Clear your site, define your drive approach. Level by backscraping with the blade. Once that's done lay out and square off your structure dimensions beginning with the corners using wooden stakes and stringline. Plant additional stakes at multiple sections along your side lines between corners. You can level the field using any type of tripod, camera tripod, music sheet stand, etc. Tape a cheap scope on the top in a way where it will pivot 90 degrees and keep the crosshair level. From there have your wife hold a length of stick or 2x4 on end with a well visible tape measure, or incremental marks you've drawn on it so it works as a ruler. Make yourself a sketch of the foot print and section the sketch like a checker board. Then have your assistant move to the middle of each 3' square you have and set the 2x end down and YOU viewing through the scope can see the measurement your crosshair is at on the board. Write down each measurement as she positions herself at each 3' square location. From there you can use that sketch to determine where to determind the mean average "middle" height you need to readjust the surface dirt to level your foundation pad site. You can do this by shovel full at a time. Once level to your satisfaction (remember, it doesn't have to be perfect, just close enough for pour'n a concrete pad which will ultimately level itself as it's worked into the form).
Here's the fun part. Now, measure an 18 inch inner offset line of the perimeter you laid out. Then dig that inner offset perimeter down to about 2 ft. Don 't go outside your exterior perimeter line. Once that dirt is removed, take 2x6 lumber and build yourself a frame to encompass the perimeter string line. Attach your framework to each stake you've placed around the perimeter with screws. Check periodically that your framework is level. Get it as close as possible to perfect as you can. Once the framework is level, complete and secure, this is when you become your own general contractor.
Get on the phone and call a couple to three concrete companies. Don't speak with the employees, speak with the owner. Tell him what it is you're wanting to do. Ensure he understands you are not a commercial entity, just some old fart try'n to build himself a man-cave to keep from going insane. He'll understand. Ask what his cost is to deliver 'crete to your property. He'll give you a better price than most who ask. Then ask him how much it would be if the governor doesn't know about it. From here he will ask you more questions and chat you up more about what it is you're doing with it. He's feel'n you out to see if you're gonna squeel on him. Insist this is all purely out of your pocket with limited income. He may tell you he'll get back with you on his answer. What that means is that he'll check his schedules to see where he's got crete headed in locations near where you live. All concrete projects have overages they deliver to site so's not to fall short when filling forms. When he calls you back he'll ask when it is you'll be ready for the mud. Commit to a date. He'll then give you a most sweet offer that'll astound people if they heard about it. Vow to keep it a secret or you'll end up screw'n yourself for other services in the community if the secret leaks out. What he'll do is not send one truck but there will be multiple trucks arrive on that date with overages they'd otherwise have to pour into a hole and bury... anywhere from 3 to five yards of crete at a time. He will schedule his deliveries at all locations to account for set up time between your multiple pours so you'll have time to work it and not cause yourself any problems, plus give you and your novice crew time to fuck around with it between each delivery. Have your crew of young teens handy, motivated, and preped with what to do when the truck arrives. Then be ready and wait. It might take a good portion of a work day but it'll be done and over with and the cost will run remarkably small in comparison to what you'd normally have to pay. I did a 30x50 6 inch slab with 2ft thickened edge for 4,000 which included my lumber, the bobcat rental, rebar, tie wire, sill anchor bolts, pay for the teenagers, one experienced concrete worker's time (mostly in beer and bbq), the crete and delivery cost, plus finishing the crete to a smooth sweet finish (it looked polished!). And while ea. truck was pulling out, and the crew was getting each load level to the form sides I placed the sill bolts in place precisely in the middle where my wall sill plate would end up sitting. It went smooth as silk, i swear. That foundation, otherwise, at best cost paying to have it done from scratch would have cost 15,000.
Once the slab is finished you can then take your lumber and stage it onto the flat surface and begin to fabricate your own walls. I did this in 8 ft. wall sections. Each were framed, sheathed, and hole cut for wiring. Doorways framed, windows framed, all headers in place, etc. When I had a whole side wall ready and staged I drilled my sill plates and put them in place and bolted each down, ensuring no bolts or nuts protruded above the sill. Then I had the wife help me tilt each 8 ft wall section up and onto the sill plate where I toenailed each into place. The next wall section went up the same way, also toenailing that onto the side of the previous one up. After two wall sections are tacked, I took scrap boards and used them as props to steady and plumb the wall sections upright. Continue this way all around the slab and in very short order your entire shop wall will be completed save for the trusses and roofing.
Now, remember the lesson on getting crete for cheap. You can do very similar with the lumber package and truss package, as well. If you know of anybody who's a good friend, co-worker, or good acquaintence who builds homes for a living you may be able to get them to call in an order for your shop and they will tell the yard they'll be sending out a new guy to pick up the load and that you will be paying for it. They do this all the time for friends, by the way, who are building small shops and garages or additions onto their own homes. The discount they will give is phenominal compared to what a small contractor would get doing renovation projects. What I'm saying here is... from concept to completion, ALL costs combined, starting with the rental of teh bobcat, to final paint and wiring by a local electrician ata sweet cost of 450 bucks, btw... total price for all was 25K... for a 30x50 shop, 13 ft eaves, full 6" thickened edge polished slab foundation, 50 ft lb snowload roof, wiring, outlets, switches and bulbs, including two man doors. I built twin double wide barn doors out of wood left over that I hung. That shop otherwise... by multiple contractor quotes, was least priced at 68K (for a pole building), to as high as 87K for a stick framed structure like what I built. Any bank or credit union will give a signature loan up to 27K (or higher) depending on one's credit rating. I did the 27K loan. Once the shop was built I refinanced my property to a newer value and pocketed about 30K into our savings account. My original home loan was for 156K... the new value of the property went to 187. Realestate market value on the property is now at 250K. Just a little sweat, creative thinking, and ferreting out resources and organizing people and friends time, make'n new friends, etc., I pumped up the equity in my home big time and gave myself a man's dream shop to grow into.
You, my friend, can do even better considering your smaller footprint you desire of your perfect shop.
Just say'n... dream big... go big, or at least as big as possible within the research of resources you have available. I took pictures of each and every step of construction so's to share with others who might wander down this trail. Ended up moving and building another home, also out of negotiation techniques described above. I now own a home I got loan to build at 232K. It's value, with the add on 30x40 shop I built precisely as described above, puts my home value now at 300K. I took pics of this home's construction, and my shop's construction at each step of development as well. I'm here for ya to advise if you have a mind to listen.
Best of luck to you, Jammer. All good things come to those who wait and persevere.
