Now, assuming that you have build project at hand, how to proceed?

First, decide how you want to use the bike. Be honest. More for show than for go? That's valid.

Second, decide on an overall budget. Then get some feedback on what is doable with that budget. Perhaps a titanium frame or an XTR group is out of the question with a $500 budget. You get the idea.

Third, break down the build into sections and start to explore each section, paying attention to cost. You will fairly quickly come up with a list of parts.

Fourth, get some feedback on the overall build - how the parts inter-relate and cost effectiveness.

Fifth, go for it.