It isn't worth making your own pc nowadays? Yes it is look at the money you can save.
To the point £500 i'll see what i can do
I made the pc below on pc specialist.co.uk it comes to £530. Just a little bit over your budget but a not bad pc.
Case
PCS MAELSTROM T900 BLACK GAMING CASE (£59)
Processor (CPU)
AMD ATHLON II X4 630 (2.8GHz/2MB CACHE/AM3)
Motherboard
ASUS® M4A78LT-M LE: DDR3, S-ATA II, 1 x PCIe x16, 1 x PCIe x1, 2 x PCI
Memory (RAM)
4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Graphics Card
1GB ATI RADEON™ HD 5750 PCI EXPRESS - DirectX® 11
2nd Graphics Card
NONE
Memory - 1st Hard Disk
500GB SERIAL ATA 3-Gb/s HARD DRIVE WITH 8MB CACHE (7,200rpm)
2nd Hard Disk
NONE
RAID (HDD 1 & 2)
NONE
1st DVD/BLU-RAY Drive
24x DUAL LAYER DVD WRITER ±R/±RW/RAM
2nd DVD/BLU-RAY Drive
NONE
Memory Card Reader
INTERNAL 52 IN 1 CARD READER (READS XD, MS, CF, SD, etc)
Power Supply & Case Cooling
450W Quiet Dual Rail PSU + 120mm Case Fan (£25)
Processor Cooling
STANDARD AMD CPU COOLER
Sound Card
ONBOARD 8 CHANNEL (7.1) HIGH DEF AUDIO (AS STANDARD)
Network Facilities
ONBOARD 10/100/1000 GIGABIT LAN PORT
USB Options
4 x USB 2.0 PORTS @ BACK PANEL (MIN 2 FRONT PORTS) AS STANDARD