Hi.
A "custom" instrument case ATA-style:
Making a custom case for Epi LTD Explorer
Tips?
If You want to save money: You probably won't.
If You want to make something that has resale value: You probably can't.
You'll need some tools or an access to a wood-shop.
Not everyone will allow You to use their saw for cutting aluminium extrusions.
That said, You roll your own, you can:
Make the cases to fit your car for example.
Maximize the use of space.
Make cases that aren't available on the shelf.
Make cases that protect gear better than what's generally available etc.
Nothing obviously prevents You from making cases other than ATA style. That usually means much heavier construction and/or necessitates use of special tools/equipment though.
Regards
Sam