I have a dormer window with a flat roof above then roof tiles. When ever we get strong wind and rain from a particular direction I get water coming into the bedroom. I have decided this is because the roof felt does not go very far under the roofing tiles and rise up the battons above it, only about 50mm so I think I need to glue some felt to it to extend it up and behind the roofing tiles (Double Roman). Flat roof is about 3m wide so I basically need a piece of felt about 3M by 0.2M I would guess, maybe Self-Adhesive Flashing tape or torcheable felt?
Any ideas would be appreciated, the other complication is that I have solar panels above that need to be unclipped to access the first row of tiles. These seem to be bolted to the support brackets and I believe plugged together.Access is easy so I am assuming I can turn off at the inverter and temporarily unscrew and place on the flat roof while I work (wearing insulating gloves and a cloudy day)
Any help would be appreciated.

panel / /\
/ / \
/ / \
____________/_/felt\
|dormer
|

Steve