Definately DIY. There are some great posts of people's self built racking systems in the DIY section here. I built a rack myself with very modest technical skill and no experience building furnature. Turned out great! Melamine is the way to go, get the place you get it from to cut it for you, then all you need is a drill to put it together. Make sure you predrill your holes, and use appropriate screws. All the instructions you need for building a rack and wiring flexwatt are out there and generally easy to find and follow.

As for tubs, most people use 30 or 32 qt. tubs for adult males/smaller females, and 41 qt. for bigger females (1500g+) I built my rack so that it fits two 30qt Isis tubs side by side on each shelf, or one 50qt Isis tub widthwise, incase I end up with a snake that needs more space than the 30qt, but so far all my females fit just fine in the 30s. I also don't plan on having an excessive amount of snakes, just this one rack, so I built the top shelf 2 inches lower, which means that the 6qt Isis tubs fit 4 across on that shelf. But that's just me, most people seem to have seperate hatchling racks, but that's unnecessary for me at this point.