how much garage space needed

With bigger long term plans for the shop, In order to store 15 to 20 cars, you are looking at about 3600 sqft

I got that number by calculating approx numbers as follows:

20feet long (room in front, room in back)
12 feet wide (average car being 8feet wide, with 4 feet for an open drivers door)
15 cars
20*12*15=3600

now, if you wanted space to work on them all, maybe shoving 5 or 6 to a corner, you are looking at about 4500 to 5000 sqft

 

The answer will depend on the layout of the space and how many doors you have. My place is 40 x 100 for 4,000 ft2 of space, but the two doors are on the same 40 ft wall. So I have to leave a lot of open space to get to any one car without moving another car out of the way. If one of the long walls were all doors, then the cars could be packed much more efficiently.

The neat trick I saw here a few months ago is to make a scaled floor plan of the warehouse on a piece of paper and then cut out some paper rectangles to represent the cars. Draw on the door locations and then move the pieces of paper around to figure out how many cars will fit.

 

You can download a 2D / 3D design software that is easy to use. I did this to design a garage and it actually had about 20 different cars, including a F430 spider, that you simply drag and drop into the plan. Also cabinets, work benchs, etc, etc. Very cool as you can switch from 2D to 3D with a click of the mouse and actually go into the space looking a how the cabinets work, etc.

 

what's the name of that software?

 

I recall this as well and tried to find it last night (to no avail) for the OP.
It's also worth taking a look at garagejournal.com which is a terrific reference site.

 

I use 9,000. Center driveway. Lots of room on one end for the stuff everyone will have. If they don't now they will. That's our nature.