I have two zones of suspended 2" slab with R24 under the slab in the joist cavity. Each zone has four loops. Zone 1 has one loop that is in a room that I would like to keep cooler than the rest. Zone 2 has one loop in a room that I would like to keep warmer than the rest. I am considering going with the 4 loop Uponor manifolds with balancing valves ($600 for two of them) but I am wondering if I could get almost the same result by making my own manifolds using pex and shutoff valves. Thoughts?

While it is certainly possible to home brew manifolds, I would recommend purchasing them. You might want to consider a different brand and shop around for a better price.