When I got my Echoplex it didn't have a footswitch with it. Being a curmudgeonly cheapskate I looked for a way to build one on the cheap. Rummaging around my workshop I found a metal deck support I had gotten at Home Depot for some reason, and after a few minutes work with a hammer and a vice I had my footswitch enclosure. A little digging in my junkbox for a switch and a jack, and I was in business.
For just a jack and a switch there is plenty of room, but if you wanted to put an effect inside it you could use sides that are more narrow to make more room, or even another piece of metal. You could also make the outside bends into inside bends and put a bottom plate on it.
Things like fuzzfaces, loopers, and A/B/Y switches would work fine in an enclosure like this.
Whatever you can shoehorn inside it is worth trying, it's a 99 cent enclosure!!!