I have only built two...and had a blast doing it...and learned just how much i did not know (well, I am not sure i have really learned that)... in my case both were bikes I built for someone else... but watching them ride and seeing the joy of it was a great payment for me.
I started off by getting used frames in their size...and on one I ordered the controls from England (ultegra 6800) at quite a bit lower than I could find them here... on the other I used gently used components...both turned out nice. Both were rewarding in experience and emotional attachment, neither were really economically worth it.