I was once a newbie before my current rig, 4 days old only. from my knowledge tradepac is the cheapest around when I look at the pricelist as well as going shop to shop for quotations. Though you must know what you need exactly.
Basic components: (and things to consider)
Motherboard (form size, pcie/pci slots, usb3.0, RAM aka DIMM slots)
Processors (K-overclock, heavy video editing etc = i7)
Power supply (Bronze, Gold, Wattage, brand)
RAM (dual channel or not)
Graphic cards (Nvidia versus AMD, VRAMs)
Storage (HDD, SSD)
Optical Drive (Blu-ray or just a basic DVD)
Internet connection (Cable, PCI-e/PCI wireless card, USB wireless dongle)
Casing (forms= iTX mATX ATX, available fan placements)
Hope those basic list helped you. Building your rig, and researching yourself gave me immense joy and pride, hope you will enjoy it too. Ask you expert friends in regard to details, I had a expert friend and his advice was valuable. And now I'm enjoying games at high-ultra settings with a 23" monitor.
Goodluck!