I know one guy close to me that put up a metal free standing two car carport. $695 installed. He then closed in the ends and the sides. Added windows and a door. Started with a dirt floor then upgraded to crushed stone. Later he will pour concrete or PT wooden floor.

Go as cheap as you need to. I started with a 12X16 shed, then 24X24 and now a 28X32 with a 12' wide shed roof along on side for storage outside but under cover. It is now too small. You will fill up whatever you build.