My shop space is 25 deep and 43 wide,,,it is enclosed from a pole barn that I have and my shop is one end of the pole barn.
I have a 76 Vet that I drive in the summer and do resto work on it in the winter. The space gives me enuf room to work on the car during the winter and also leave space for another vehicle for maintenance.
I suggest you consider a 2 post lift for your shop,,,I have one and they do not cost a lot,,maybe 15 hundred bucks. You have no idea how much easier it is for working on a vehicle with a lift in your shop and resto work it is a must. One thing you need to consider if you do have a lift is that your 10 ft ceiling is not tall enuf. They make lifts for 10 ft clearance but you will need to make a cut out above the lift for the car to raise high enuf for you to get under the car, I had to do this in my shop since I have a 10 ft ceiling. Another important thing to consider is the area around the car,,,you need lots of room to work around the car,,nothing worse than cramped up against a wall and trying to remove a transmission or something like that.
In my opinion the 20x24 size is cutting it kinda small but workable,,,,you need extra room for a engine hoist and engine stand and somewhere to set a trani or rear end and other parts. What about a welder and cutting torch outfit, drill press and grinder and a big tool chest for all the tools you will need. All that stuff takes up floor space.
I hope I have helped
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