yes I can do it, first of all know your budget, how much are you willing to spend for a unit.
second know you parts as much as possible you must have a knowledge about each part of a computer, what they do and their importance inside.
third every parts must be compatible with one another, that is why you should know which part can be used for each.
forth there are a lot of parts seller online some you can find a bundle promo in which when you buy something from them, they could give you discount on the others, know how to canvas, don't just pick and buy, haggle if possible.