Just my .02...
I've been thinking of some custom cases for a while now, and found a guy who was making them back in '80s. Since he's not in that line of work anymore, he was kind enough to explain what he did:
Make a full size 3D template for the case out of styrofoam (you can cut it with hot wire, like on a bandsaw), just 1cm inside of actual size, to allow for the side thickness,
Cut out the top and back out of 3-4mm plywood,
Cut the sides out of 10mm plywood, for round portions make a bunch of 10mm x 10mm x case height sticks of same plywood, and stick them to a strip of jeans cloth using PVA glue (they'll look like gun rounds), and stick it to the mold,
Fill gaps between sticks with sawdust/PVA mix, let dry,
Add top to the mold, let dry, take out styrofoam,
Add back, let dry, sand off excess glue etc,
Mark opening line of the case,
Saw it open,
Take another strip of jeans, 10cm wide, long as needed to go around your case, soak with PVA, fold 3 times to get 3cm wide, thick strip, and glue around the inside of the bottom of the case to form a lip while glue is wet,
You can dress the whole exterior in jeans, also soaked in PVA (I believe surfboards are finished something like that, ofcourse not with jeans
), even mix it with some powder dye,
Fill it with foam from the bottle (for windows and such, don't know proper english word, sorry),
Cut out whatever shape you need,
Upholster it with whatever, add hinges etc...
I would probably add some braces for added strength to both top and back, he didn't do it tho... (I've probably been reading too many books on acoustic guitars...)
DISCLAIMER: I haven't gotten around making one of these as yet, so if you do, please let me know if it works
For those who need it, 1in = 2.54cm = 25.4mm.
BR
Goran