I would do something like this...Its a small setup but it still houses full size psu and gpu and h100i.
I put something really simular together for a guy about 5 months ago. It came out really nice and its pretty well portable.
PCPartPicker part list:
http://uk.pcpartpicker.com/p/2JfUX
Price breakdown by merchant: http://uk.pcpartpicker.com/p/2JfUX/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/2JfUX/benchmarks/
CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor (£161.17 @ Amazon UK)
CPU Cooler: Corsair H100i 77.0 CFM Liquid CPU Cooler (£87.99 @ Amazon UK)
Motherboard: EVGA 111-IB-E692-KR Mini ITX LGA1155 Motherboard (£134.99 @ Amazon UK)
Memory: Kingston XMP 10th Anniversary Series 8GB (2 x 4GB) DDR3-1866 Memory (£64.31 @ Amazon UK)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk (£66.98 @ Aria PC)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£43.54 @ Amazon UK)
Case: BitFenix Prodigy (Blue) Mini ITX Tower Case
Case Fan: Corsair Air Series SP120 High Performance Edition 62.7 CFM 120mm Fan (£10.94 @ Scan.co.uk)
Case Fan: Corsair Air Series SP120 High Performance Edition (2-Pack) 62.7 CFM 120mm Fans (£20.54 @ Amazon UK)
Case Fan: BitFenix Spectre 97.8 CFM 230mm Fan (£11.78 @ Amazon UK)
Power Supply: Silverstone Strider 600W 80+ Silver Certified Fully-Modular ATX Power Supply
Total: £602.24