I'm trying to put a new pc together and its the first time I've to do it and I'm struggling to spec a power supply as I blew my last one up trying to do this, it was an EZCOOL 800w ambience one though and I have now found out that they are cheep and nasty units. I will list below the spec of the machine I am building and I would like to now the size and brand that you all would recommend. I was considering a EVGA supernova 1200W P2 80+ Platinum.
 
PC spec:
Motherboard: ASUS crosshair v formula-z
CPU: AMD FX-8320 3.5GHz 8 core
Memory: G.Skill Ripjaws 8gb (2 x 4gb) 1600  
Storage: Western digital 2 TB with the possibility of expanding to a second 2 to 4 TB drive
Video: Gigabyte Windforce Radeon R9 290x 4GB
Case: Cooler Master Storm Trooper
 
I've been used pc part picker to try spec'ing the wattage on this pc but I'm a little sceptical of the result that it has given me as it has specified a total of 520 watts but gigabyte specify that the video card requires 600 watts minimum.
 
 
   

Thanks buddy ill start looking into it now.

I would also recommend at least a 850 Watt PSU for your build.

Yes 850W is enough even for OC 8350 and OC R9-290X.
But people with Radeon cards often think on Crossfire when price of cards drop.
Example R9-290X will cost 300$ very soon.  Than you will stuck with 850W.
In that case best choice is your 1200 P2.
With 850G2 you can use sleeve set and Eco Mode if need.
750/850 G2 have that switch same as 1000/1200/1600 P2.
 
 

I recommend 850w firstly because there will a headroom for more and secondly psu wattage decreases with time