I recently did a build of the BBT mining case below out of two 8ft pieces of 1/8" x 3/4" angled aluminum, one 8ft 1" x 2" piece of pine and #8 1/2" self-tapping screws.
https://www.youtube.com/watch?v=D5xNrlxsCVsThe only tools needed were a drill with a 3/32" hex titanium drill bit to drill pilot holes and a #2 phillips screwdriver bit. A hacksaw with a 32 tooth blade and a plastic miter box to cut the aluminum and wood. It took about 4-5 hours since it was my first time building one. The case is very sturdy and can support up to 7 GPU's. You could also use wood or 1/16" angled aluminum pieces if you want to save money. Way cheaper and quicker than ordering a case online.