Dormer pitch shallow

[PNE123]

I have just purchased a 2 bed dormer bungalow near Preston, pics attached along with neighbouring properties. Mine is the one with the brown wooden windows. Circa 1965, previous owner deceased and property had become neglected. I had concerns about the roof leaking when I initially made the offer and the price of the house was reduced accordingly. Rainwater was coming in, especially into the back bedroom and had damaged the bedroom ceiling boards and the dining room below. The sellers agreed to do a temporary fix so no more rain is coming in at the moment.
The survey came back highlighting broken tiles and deteriorating flashing but did not mention the pitch of the dormer.
Now i own the house and I have had a closer look I suspect that the dormers (identical front and back) were originally flat having looked at other similar properties on the street. Some houses, including mine, at some point appear to have created pitched roofs above the dormers I presume to prevent having to deal with issues with dealing with leaking flat roofs.
The angle of the pitch of the house next door is door is steeper whereas mine and my neighbours attached to me are shallower. I suspect rainwater has been driving in underneath due to the roof being shallow.
I am planning to get a reroof replacing the concrete tiles with new ones. I am just wondering what my options are for the dormer roof section. Pointless just replacing the tiles if rainwater will still drive in anyway. I was thinking one option could be a fibreglass roof for the dormer section, would this be suitable with the current pitch? Or is it better for the pitch to be adjusted to make it steeper or even back to flat roof using fibreglass or another material and if so how would this affect next door?

 

[Alastairreid]

The join between the 2 roofs would need some detailing to separate them..If it was my roof I would put it back the way it was, insulate and finish with EPDM.