There's not much that's complicated about building your own upper, special tools are not an absolute necessity either. The only part that can be an issue is getting the barrel and reciever bolted together. I've used a brass punch to tighten the barrel nut to the reciever. Just work your way around carefully until you tighten it evenly, then tighten it some more until the gas tube lines up with one of the holes. Use a big C-clamp and a block of wood to clamp the upper to the work bench. If you're lucky, you can find a budd that has the holding fixtures that will help you out. Makes it much easier to assemble, but not the end of the world if you don't.
You can find plenty of videos at Brownells, YouTube, etc that will show you how it's done. Just purchase the individual parts in the configuration that you want and put it all together.
Some folks argue that you must check the headspace with a set of Go-NoGo gages, but if the barrel and bolt are of good quality, you really don't have to do this either. The barrel extension, chamber, and bolt either line up and lock or they don't, pretty simple. If it makes you feel better, take it to a 'smith and have the headspacing checked once you've assembled everything.
