C-man,
I did this a couple of years ago for my son using things I learned from this board on TOS, the partspicker site, and a couple of articles online from PC Mag. I built for less than $900 something that would have cost on the order of $3000 if I had purchased it retail. It was much easier than I thought it would be and the stressful thing was never really knowing if it would work until I turned it on and finished up. I was like you and had never done anything close to something like this project. If I can do it, almost anyone can.
My only advice (and someone already said it) is that if you have the space, just get the biggest tower you can so you have lots of room to work with. I got one that has a lot of see through and it lights up blue so my kid thought that was really cool. Even with all of that space, it was still sometimes challenging to get everything to fit right.