Structurally, SIP capacities are easy to estimate. Span eight feet between trusses with an 8-inch panel, and you're being conservative for just about any allowable load. You can put some of that money back in the bank. You'll find additional savings when you look at overhangs. In that built-up wood assembly I talked about, framing the eave and gable overhangs takes a lot of time and material.
SIPs offer more than insulation.
They offer structural help and fast dry-in times too. Since log buildings have no cavity insulation in the walls, they need an insulation boost in the roof to meet model energy codes, and SIPS give the builder more mileage by a healthy margin. The log home industry has a whole gamut of roof structures. SIPS are compatible with all three. But if you're considering SIPS, do yourself a favor and talk to a SIP supplier before you commit to roof substructure details.