I ran a y in my shop , 120 X 40 but only have air and multiple plugs, machinery in one half, the other half is storage. I now usually only work alone but when one of my boys is working there too, 1/2 for each branch is enough. It is 3/4 out of the tank in the corner then 1/2 each way. DO NOT USE PVC . When it ages it will get brittle and can fracture or explode and the shrapnel will not show up in X rays. I did use pvc at my old shop UNDER GROUND with copper pipe coming up to have an air outlet at the front corner of the house. I had to replumb the Air system at a factory, The first install was all 1/2 pipe . when 4 or 5 air tools were running they were not getting consistant torque readings. I redid it with 2 in copper main line with 1/2 drops, and 1 inch and 3/4 for short branch runs. and 1/2 drops.