to give you a starting point:
went with a mechanical keyboard, could always be swapped to a saitek or microsoft x4.
mobo has allowance for PCI-E 3.0.
if no o/s is needed change the 64gb ssd to the 128gb version.
went with a dvd drive, maybe change it to a blue ray drive if he'd find it useful.
Asus GeForce GTX 580 DirectCU II 1536MB GDDR5 PCI-Express Graphics Card **Supplied with FREE Batman: Arkham City PC game** £389.99 (£324.99)
Asus ML249H 24" Widescreen LED Monitor - Black £191.99 (£159.99)
Intel Core i5-2500K 3.30GHz (Sandybridge) Socket LGA1155 Processor - Retail with FREE TrackMania 2 Canyon PC Game £179.99 (£149.99)
Asrock Z68 Extreme4 Gen3 Intel Z68 (Socket 1155) DDR3 Motherboard £159.98 (£133.32)
Corsair Enthusiast Series TX750M High Performance 750W Modular Power Supply (CP-9020003-UK) £99.98 (£83.32)
Microsoft Windows 7 Home Premium SP1 64-Bit - OEM (GFC-02050) £79.99 (£66.66)
Crucial RealSSD M4 64GB 2.5" SATA 6Gb/s Solid State Hard Drive £77.99
(£64.99)
SteelSeries 6G v2 Mechanical Gaming Keyboard (64226) £69.98 (£58.32)
Samsung SpinPoint F4 EcoGreen 2TB SATA-II 32MB Cache - OEM (HD204UI) £60.98 (£50.82)
BitFenix Shinobi Gaming Case - Black £49.99 (£41.66)
Corsair XMS3 8GB (2x4GB) DDR3 PC3-12800C9 1600MHz Dual Channel Kit (CMX8GX3M2A1600C9) £49.99 (£41.66)
Gelid Tranquillo CPU Cooler (Socket 754/939/940/AM2/AM2+/AM3/LGA775/LGA1155/LGA1156/LGA1366) £25.99 (£21.66)
LG GH22NS70 22x DVD±RW SATA ReWriter (Black) - OEM £17.99 (£14.99)
Sub Total : £1,212.37
Shipping : £20.10
VAT : £246.49
Total : £1,478.96