Open roof with single sloped parallel trusses

This is a homeowner forum question, not a rebate or policy update, so there's no broad news to report here. A Colorado homeowner planning a new 28-by-28-foot building for a home gym, theater, and golf simulator is asking for advice on roof design. The building will have a single-sloped roof (a shed-style roof that slants one direction) built with parallel chord trusses, which have a gap between the top and bottom framing members roughly 2.5 feet deep. Walls run 10 feet tall on the low side and 15 feet on the high side, with a shallow 2:12 slope.

The homeowner wants to skip an interior ceiling and leave the truss space open to the room, and is asking whether that works, and if so, how to handle venting so moisture and heat don't cause problems. One option raised was spray foam insulation applied directly under the roof deck, which would create an unvented, sealed roof rather than one with airflow between insulation and roof sheathing. The plan also includes a mini-split heat pump (a compact, ductless system that both heats and cools) for climate control in the building.

For a homeowner following energy-efficient construction, the takeaway is mainly a reminder that roof design choices, especially whether a roof cavity is vented or sealed, affect moisture control and insulation performance, and are worth getting right before construction rather than after.