Hey. Newb here, but my input...yeah make your traps. I built similar and find them indespensible in my room.
I built 4 in total. each uses 2 slabs of roxul for a thickness of 6". The boxes are built to the exact size of the roxul slabs.
I used 1x8 pine boards. Corners are mitred, glued, brad nailed, and braced on the inside with right angle metal brackets.
Here's one stuck up in a corner. Does a great job removing the bass flutters when we jam.
I built 2 with hardware for hanging in the corners. The other 2 have feet and are used on the floor. Mainly, they serve well for blocking guitar cabinets. I found that the guitarists needed their cabs too loud to get the right sounds for playing, so I use the traps in front of the cabs to block the noise. Then I place a SM57 between the trap and the cab, and route sound thru the mixer and into floor wedges. This way each band member can have the volumes controlled to a level they like, while the whole room doesn't suffer from competing guitar cabs. The 6" of roxul really blocks sound nicely.
Here's on under construction. The 1/4 round serves 2 purposes. The first, is to give the trap a nice finished look. The second, is something to staple to fabric to on the inside. Then fill with 6" of roxul and staple another piece of fabric over the back and done.
Super easy to build if you have any carpentry skills. The level of finish on them is up to you.