Well before going about it that way, I seriously suggest setting a budget and then picking out all the components around that. Because then if you need the extra $20 for a CPU upgrade, you can make a small compromise in other areas. I don't usually suggest buying components one at a time and trying to put together PC that way.
As well if your interested in the help, If you post your build and planned usage I'm sure you could get some great insight here. But if not, good luck!