[JA]

^ A white painted roof is a good way to go to reduce solar radiant heat effects as is (High shade percentage) shade cloth!

If you're building and wanting a metal roof, then white colourbond roofing would be better still. Also keeping your white roof clean will maintain its high reflectively, which is easily lost by dust, dirt and leaves. In terms of reducing any transmitted heat then sure, use insulation (foam sheet seems a good idea) and if you really want it cooler, then close all openings. All though you may want to have a controllable opening with fan to extract warm air/ pressure relief as it slowly heats up and or control any excess humidity as it will over time effect equipment left in place for extended periods.

Best
JA