20' deep is not going to leave much room for a large car or a truck. 10' wide won't leave room on either side much either, so your stuff would need to be easily moved around.

don't worry about damage to teh roots from a slab, worry abotu damage to teh slab from teh roots.

if it were me i would decide whether i wanted to use it as a garage and lose some trees, or keep the trees and park elsewhere. maybe you could put a carpot off teh front/side of it and just park teh car there? gotta have the room in 1 direction, as you must be able to drive up to it.

I am planning on making a 2-carport on the side of the house. I still need a workshop to put all my tools (table saw, miter saw, band saw, belt sander, etc.) so I can use them. Currently all the big tools are in boxes and I take them out to do something and have to put them back afterwords. Its a PITA!

Thats the reasoning behind trying to get rid of the tool shed and replacing it with a bigger workshop. I was then thinking that if it was big enough to get a car in, then I would be able to do any emergency repairs during the winter (I live in charlotte and the winter is only about 2 months long)

The site is about 12 feet from the end of my driveway and I could drive the car on grass to get to it in case of an emergency.

I am looking at metal and maybe structural concrete for a floor that might be able to handle a 4000lb car.

I know I might have to come down to earth and realize that getting a car is asking for too much given the constraints but I at least want a stable-solid enough floor to handle the power tools and the vibrations.

Thanks

if you give up on the idea of getting a car in it, you can get a good 12x20 shed on skids for 1/3 the price or less of putting one in that would support a car. and it will handle the tools just fine. like i said, you cna put a carport off teh front of it if necessary. i have seen folks get the metal carports with sides and set them over gravel. this keeps you off teh ground, and provides decent protection from teh elements. or you could custom build one that perfectly matches the shed. your choice.