question about new install

Planning on new home construction soon. Home will be approx. 3200 sq feet. Walls will be ICF. Home will be in Oklahoma. Thinking of using steel shingles. Will be a DIY project. My thought was trusses, then decking, synthetic underlay, eps, 1x4's, more decking, then underlayment, and then the shingles. Is there a problem with this? Is it overkill? Just thought it would be nice to have a cool roof. Under the roof deck will be sprayed foam insulation with the attic being a conditioned space.
Thanks

What is the insulation level going to be in the roof? While foam and exterior insulation performs much better than fibrous, the reality is that code is code and they will probably hold you to the letter in terms of what you are required to have in the roof assembly.

Between you and me, 2-3" of exterior foam on the roof in an above deck ventilated design works fantastically, the code enforcement person is just going to use a chart to check what it "should" be.

If you aren't worried about the code part of it, if you can get 3-4" of foam in that roof assembly, it would work like a drean.

No codes where I live. Nobody cares. Insulation man told me he could spray then layer of closed sale then open sale. Probably 6 to 8 inches. Was thinking the eps would create complete thermal break. Was worried with our storms/wind that it may not be wise to put the air pocket between the 2 roof decks though?

You are spot on. Just like your ICF construction, moving the foam to the exterior minimizes what you need to install on the inside because of the thermal break and the convective cooling in your case as well.

If you can get like 3" of foam in that exterior, he might not have to spray anything on the inside if you are aren't worried about code.

3" of XPS = R16

That will be about as good as your wall at that point and with the convective cooling...you should be AOK.

Just make sure the attic is properly conditioned and you won't have any moisture issues at all.