Mansard Roof

Take a block with suitable texture

Use the surface-edit (on my keyboard it is the Alt Gr key) and change the shape so the lower end remains in width and the upper end is more narrow.

close surface editing and use the regular resizing-possibilities to have a thin board, rather than a block

now you can fiddle around the "block" to allign with each other to the roof you like

i think this is the best i can explain it here. the key is the surface edit mode through which you can individually change the shape of one side (the upper) of a block.

Avanar already gave you the easiest method. Create a complex roof is never easy but it's also possible to calculate the shapes (with a spreadsheet) to do a fine work with console commands. If you are interested (and not afraid by numbers) I can share my spreadsheet and try to give you some explanation.

Just a quick and dirty example of what i mean:

It is not easy to find the right angle. Small gaps can happen, if you are not working 100% accurate, but can be covered with beams or similar that cover the corner anyways. Or you follow the accurate path of Ozorvals with a spreadsheet.

Still it boils down to fiddling around with it. Roofs are a science on its own - there is no easy way, if you want it to be good