Stuff like Model Pack 3 (M3) roofing can be a little hit and miss when you 1st see it, but soon becomes very logical.
What you may not notice is that the roofing is an overlay set and you actually place some parts all in the same grid square in the editor. As for the 4 arrow cross marker when laying down the roofing sections, just place one in an empty spot to see it's direction, then rotate as needed. You will soon get the hang of it.
Also the edge bits you apply in the adjoining grid square, as they sit on the very edge of the 4 arrow marker.
I only use this for fun and have no interest in making commercial games ^_^