Friend is looking for idead how to make or buy a way to stack ATVs in a garage to maximize space. Any links or projects are appreciated.

Check on the sled sites I know there is some thing like what you are looking for that stacks sleds.

#1 sled storage

#2 store bought

I would look around and see if there are any places near you that sell commericial or industrial shelves. That was what I was thinking of going with. Or you could build one out of unisrtut, depending on how handy you are. I think unistrut would handle it, I have put a 1000 pd transformer on unistrut racks.