well you could have the 20 long on top, and the 20 high underneath, and have storage / bookshelf area on either side.
problem is, unless you elect to have one tank rather low to the ground, it will be difficult to provide "access room" to both tanks and keep the height managable
the only kind of stands I know how to build are brute force "utilitarian" stands, composed of 2x4's and lots of screws... my guess is you're looking for something more finished looking.
look into 3/4" birch plywood as your construction material, using a good glue and well placed screws, it should be able to hold the weight of a pair of 20's with no problem.
here's a diagram of what I'm talking about - it's basicly just a plywood box, with some extra dividers/supports inside
you could build it out of something like 1x4 paneling and then cover it with some 1/4" veneer as well, but solid plywood would be much stronger (and heavier)