You can pea into a bush out back, you can use a big fan, you can heat with all sorts of devices. One thing you can not do is build big enough, you will fill what ever space you build.
Put everything on wheels, to this day I still move stuff around depending on whats going in and out of the shop. It is nice to be able to pull the door down on your project when your done for the night.
I have a heated shop, never sprung for A/C, heat runs for 6-8 months out of the year, Radiant Floor heat, so nice to lay on a warm floor. I have it well insulated also with insulation under the slap as well, reflective, and I don't think foam does well between rock and concrete. I also planed for a two post lift. But really like my EZ car lift as I can move it around. Clear floor space is the key for me.
Don't forget about tunes
Don't forget about Fire Suppression, I have several extinguishers stationed all around the shop. Mounted to my welding carts, and tool boxes.
Don't forget about safety gear.
And map out a clean side of the shop and a dirty side. Clean at the back away from the doors, dirty by the doors, that way you can take a leaf blower and start at the back and blow the garage out towards the dirty crap. Also cover everything when not in use. As you get into bigger projects and more tools, think Mills and Lathes, it is nice to just uncover a tool, and start working. Not clean, fix, delayed, then get to work.
Put everything back in its place when done using it, keeps your mind like water. And never misplace a tool or part again. Also makes you more productive. I have a small cart I got in an auction that has three shelves its about 24" x 24" x 3' tall, and it use it while working on a project. Then when done, I take my tools back to their homes. I strive to do this with everything.
Also plan on lots of storage, for large and small items. If you plan to do car repair or restoration, a car taken apart takes a much larger area than a car assembled. Yeah I know that right, you would be amazed at how much space it takes. I have 50 or so tubs, that hold sections or parts of the car. Engine compartment minute the entire engine is in three tubs. Rear Trunk has a tub, Suspension is done by corners, and not everything is in a tub. The advantage is I pull a tub to the side I am working on, everything is in the tub except like trailing arms, and I can get to work. Wheel over my little cart, all the tools I use go onto it until the job is done or I switch sides. I'll more than likely use the sam tools on the other side.
Buy the best tools you can afford, and treat them with respect and kindness cleaning them as you would if they where plated in gold. They will last for ever.
YOU CAN NEVER HAVE ENOUGH TOOLS
so plan ahead, I would rather have an empty drawer or two than run out of room, and have stuff sitting on the work bench, cluttering up space.
I store seldom used tools in bins by the jobs they do. So you will see all my concrete tools in a bin, if I am working on concrete project the bin goes along with me. Same thing goes for paint guns, A/C tools, electrical tools for the house etc.... I have a set of hand me down tools at my house for my wife, kids and myself to use. That way I don't need them to be in the workshop digging for a tool, when they can grab the backpack off the shelf, and they have all the tools they need for basic repairs.
If your storing things up high, a rolling scaffold is very nice to work off of. Takes some floor space, but I park it over the top of my spare engine and trans, when not in use. I also stack a few tubs on it for projects I am working on.
Besides a lift of some kind, a gantry crane can be really handy. The Harbor freight one is actually pretty nice. And it will save your back a lot of the times when moving larger objects.
Lots of power outlets on all walls, Quad outlets at each location is super nice, and don't cost much more to install.
Lighting, go LED 4Ft. tubes great lights, easy on the engird bills, can be retrofitted into cheap housing. Calculate this out and make lighting zones. As you get older you need more light, so plan ahead your future you will thank the past you.
Big Ass ceiling fans and lights - thats all I got to say.
don't forget about wheels and tire storage, my garage currently has 16 wheels for my 914, looking at adding a couple more for matching trailer. And my Jetta has 8 extra sets, though after this winter one set will go away.
Place to store an extra bottle of Argon or Argon/CO2 mix. You will always run out when the gas supplier is closed.