when you do the last layer the joints should go against the slope,
but the important bit is to get a good seal on the joints, it's done by melting the edge of the felt, ps when I say melt whot I mean is you put heat on it till it goes soft and the surface starts to run, I have found that you need a lot of heat as its a large area and the felt cools down fast, take my advice and hire a large gas powered heat gun, and keep it on the move as it will burn the out side of the felt and not have time to soften the center,
