Good, or bad build?

MEM - I was going to tell you to opt up to DDR3-1600 CL9, but I see that motherboard will only support up to DDR3-1333. IF you go with that board, then reduce the latency to CL8 or even CL7. Also, install memory modules in pairs to take advantage of the dual memory controllers. Installing just one modules will have you in single channel mode.

MB - Consider upgrading the board to a 970 series with better memory support like the GA-970A-D3. Gigabyte is a good choice, as is ASUS.

PSU - Antec, XFX, Corsiar or Seasonic... No EX DISPLAY! 450w is enough power, but I would opt up to a 550w model simply because the costs are similar and you have more headroom for upgrading (if needed).

HD - The laptop hard drive is fine and all, but it won't perform like a 7200RPM 3.5" drive. If you still have Samsung drives available, then look at the Samsung F3 500GB / 1TB. Seagate would be another good choice.

in that case im going to opt for a cheaper processor. The g850 as intel gives your more upgradeable options.

Yes, do not cheap out on the psu my suggestion :

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Pentium G860 3.0GHz Dual-Core Processor (£47.94 @ Aria PC)
Motherboard: MSI B75MA-P45 Micro ATX LGA1155 Motherboard (£45.30 @ Scan.co.uk)
Memory: Mushkin Blackline 8GB (2 x 4GB) DDR3-1600 Memory (£31.57 @ Aria PC)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive (£40.42 @ Aria PC)
Video Card: MSI Radeon HD 7770 GHz Edition 1GB Video Card (£85.00 @ Amazon UK)
Case: Xigmatek Asgard II Black ATX Mid Tower Case (£28.31 @ Novatech)
Power Supply: XFX ProSeries 450W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£36.98 @ Novatech)
Total: £315.52
(Prices include shipping, taxes, and discounts when available.)

If you are wanting something worth upgrading, I'd opt for an Intel system. Also, don't put parts in your system that you are planning to upgrade and toss anyway. You could save money on the cpu for sure, but Ram, Motherboard and Psu are things you'll prolly want to spend more on to allow for the upgrades to be used to full advantage. I'd also get a decent hard drive(i.e. WD Caviar Blue) that you'll be using for several years to come. Something like:

PCPartPicker part list: http://pcpartpicker.com/uk/p/wyw2
Price breakdown by merchant: http://pcpartpicker.com/uk/p/wyw2/by_merchant/
Benchmarks: http://pcpartpicker.com/uk/p/wyw2/benchmarks/

CPU: Intel Pentium G2120 3.1GHz Dual-Core Processor (£69.85 @ Scan.co.uk)
Motherboard: ASRock Z77 Pro3 ATX LGA1155 Motherboard (£76.00 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£34.98 @ Amazon UK)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive (£43.87 @ CCL Computers)
Video Card: XFX Radeon HD 7770 1GB Video Card (£86.12 @ Scan.co.uk)
Power Supply: Corsair Builder 500W 80 PLUS Certified ATX12V Power Supply (£45.08 @ Ebuyer)
Total: £355.90
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-01-08 20:47 GMT+0000)

A tad bit higher in budge though. I also don't know how much your case will cost you. Also, will you be wanting to possibly crossfire your video cards when you upgrade?