What do I do with fascia boards when putting a new upvs porch?

I am looking to put a small porch on my back door. The back door is from an single storey extension in a recessed area, so I am basically looking to close that area in for heat conservation and somewhere to put boots etcthat i don't want in the house. The clearance above the back door is sufficient for a porch etc, however there is a fascia board and associated guttering there and also along the wall forming the recess. What is the best way to deal with this? I assume I need to remove the fascias etc... Should the glass/poly carbonate roof form an overlap with the roof tiles so the rain water will use the guttering on the front of the porch... what about on the wall which will become a side wall to the porch... obviously I don't want to cause leaks and damp. Thanks