When building a comp...any comp...the 3 MOST important parts are these:
1. Case...whether you are air cooling or water cooling get a case with room for growth, great cooling, and case exterior connectors where you are going to want them.
2. Power Supply ...this run the show...get a PSU that will easily drive w/e you have in comp or MAY decide to add to comp. Consider wattage AND amperage.
3. Motherboard ...EVERYthing ur comp does, it does on or thru the motherboard circuits...you skimp here, you WILL regret it, down the road, or from day one.