If I were to create a custom water loop for a 1080 and a 6700k what is recommended?

A triple rad will fit up top for sure. I have also seen people mod the front for a dual rad. If your just staying with one GPU, then the 360 should work well. If your interested there is a res/pump combo for sale in the market. Just depends on what YOU want. I love my old Cosmos, it was the first version.
http://forums.evga.com/I7-5930K-ASUS-X99-PRO-USB-31-D5-Pump-Combo-X99-Krait-LAMPTRON-CORSAIR-SP-m2554770.aspx