Enrico,
I put it in the lower roof slab as that is the one that will show the skylight above in floor plans.
You can adjust the edges of the roof by selecting the roof, click on the edge of the hole when you get your mercedes cursor
click on the top right pet palette button (edge settings) and the Roof Edge window will come up. Set the angle for all the hole edges individually or in one step by clicking the 'All Edges' box.
If the skylight moves, remember to show both roof layers and use the marquee to move the hole in the other roof with the skylight.
HTH
just saw quick-draw Thomas' post
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"