I build lofts like this in every shop i have. Mopeds and cyles are just way too bulky and inefficient to store any other way. This one is in my pole barn, after building it i filled the top with mopeds and boxes of parts, and the bottom is full of motorcycles and heavy shit like garden tractor rototiller and stuff.
its tough to beat 2x4's and plywood for cost, i think it took me about 3 hours to build this and i'm probably into it less than 75 bucks. 20$x2 sheets of plywood and about 10 2x4's give or take. I built this one with 2x6's around the perimeter because its a big boi. (edited)