I have decided to go a for a custom setup too, just saving for it.
Since I have the Silverstone Raven 02 I know I can stick a big rad in the bottom but I want the fans no more than 800rpm and to my understanding I will need at least a quad rad for an i52500k and a 6950 both overclocked to keep temps and noise down.
So when the pennies permit I will be getting...
XPSC Raystorm cpu block
XPSC RX, or maybe the SR-1
a D5vairo pump
tubing, fittings etc
4 Scythe GT's
Fan controller
For the bits above it seems to add upto around the £270 - £300 mark and then later on I can shove a GFX block or 2 in there.
Now the Raven is going to be meeting Mr. Dremmel at some point too to chop the bottom out and at work I can make a mount for the fans and rad which will enable me to use the thicker rads. (The raven has a raised part in the bottom of the case for the 180mm fans so they need to go for a thick rad)
I may even go for a 2 240 rads in the bottom as I know I have the space, 1 for GFX and one for CPU but I have no idea if this will be better than just a quad.
Have a think about your options, draw up possible loops that will work in your case and to your budget and see what will work.
Hopefully my plan is for my system can give you a slight insight and help you come to a descision for planning the loop path.