It actually relates to the level that you reference your construct to. The elevation then, is useful if you have multiple roofs at different elevations. You may want them in the same construct so that you can merge them. I am not sure how this differs from the plate height though.
Being a devoted Roof Object user I'm rather ignorant of roof slabs. It's always confused me and seemed to be defective. OK I set the elevation at my floor level (as with the Roof Object) and then set my offset. But then the elevation jumps up too? On a RO the elevation represents the Floor level (of the RO as a whole), the edge height, the distance above that floor line.
I also don't like how a change in pitch alters the length. Real PITA for trying to set up slopes in a driveway etc.(slabs not roof slabs but the same issue if you change the pitch of a roof)
Hatch display is seriously weird too. I generally have to alter the cut plane to be able to see hatching.
For residential work the RO can be a much more productive tool though it does have it's shortcomings (less than you thnk).
Both objects are way overdue for some serious overhaul I'm hopeing soon. I'm also panning for gold in my backyard!
cheers
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