I love the custom cases and I used to be into doing similar things myself, but I found that I needed to reduce the amount of space that my collection takes up, instead of increasing it.
The best solution for me is the 'Ultimate Game Library' binders.
They hold 32 GBA games. They are
really tough to find now and usually demand a pretty penny on ebay, but I have two of them and they hold my entire GBA collection in about 5 inches of shelf space.
Coincidentally, I just watched this video last week and I like his solution (this is exactly how I store my GB and GBC games).
BTW, I love to talk about game storage and sometimes my posts about it are too long!