Check out the Boomerang swaps on this board. They are a good blueprint for your swap. We give each participant a fat eighth of our focus fabric and everyone adds their own fabric and makes whatever kind of block they like. Then the blocks are returned to their original owner. You can get a fantastic sampler quilt made from the blocks you get back.
Seven blocks isn't much for a quilt. How about doing two each, so you will each end up with 14 blocks to play with?