Minimal space would be the length of the longest solid or assembled flatcomponent: as in spar or fuselage length. If the wing is built in two pieces and then joined you can get away with half-a-wingspan of table space UNLESS the plans call for the parts to be joined with one tip elevated a certain height to form the proper dihedral (in which case the floor is handy). I have a 48" x 18" end-grain balsa building board that is a wonderful surface to build on.

I have a 4' x 8' table, 3' x 5' bench, 3' x 3' saw table surface, 2' x 3' radial arm table surface, 2' x 4' charging bench/electrical area and I STILL run out of room! Crap expands to fill all available surfaces so enough is never enough.