You can use create a space from a plan, and then alter the flat roof, or you can make an empty space and draw the geometry from scratch. As far as curves, keep in mind that Sketch, OpenStudio, and EnergyPlus don't have curved surfaces, but rather you use segments to model a curve. Is your roof curving in plan, elevation or both. Either way don't oversegment the curve or will have a negative impact on simulation time. There are a number of generic SketchUp tutorials on making curved geometry. Here is a video I made on complex geometry for OpenStudio.

One thing you will want to keep in mind if the roof is translucent, windows need a base surface to host them, so first draw the roof as solid surafces, and then use SketchUp's offset tool to create windows. You need to make sure that windows are rectangle or triangles. I typically add a small sliver up base surface between adjacent windows. If I can track down and old tutorial that shows adding a glass roof to a semicircular space I'll post some images from it.