help designing a roof

Ok so I built a summer house 5m by 3.3 and it has a felt roof covering osb, However I dont like it because its a lot darker than I thought so I want to redo the roof. Currently it has only 6 feet wide french doors in to let in light and its pretty dark because they are west facing.The pitch itself is 15 degrees

I really want to let some more light in so I was thinking poly carbonate sheets, but I really don't want the whole roof poly carbonate, is there a way to do half the roof poly carbonate? so 2.5m by 3.3? I have seen that a few conservatory's are lower where they join a tiled roof does that mean I would have to raise the half of the roof?

My second idea is to design some kind of hatch that opens out in the summer letting the sunshine in directly as an open roof, does anyone know of any designs I could copy for this? I am concerned that the low pitch will mean the water will pool around the flashing and not drain out. I have looked at the roof windows and I was thinking of something bigger like 2.4m by 1.2

Third idea would be to have half polucarbonate and half a roof deck with decking, but how would I water proof under the decking to allow the water to drain?

Also I wish to put a chimney in at the lower end of the building where the water drains, how can I make sure the water doesnt pool there and drains around it?