Yes. Ally plate forms very well [dont buy something too thick, try 20 gauge or similar. Try making a template first so as to get an idea of what size you will be needing and form the plate on a bench [kitchen table perhaps
] and once its pretty much there, put it inside the damaged area.
Then begin fixing it to the roof with the rivets, one by one along one side, following it around the plate so that you dont get any 'bunching' and they will likely pull it to pretty much the shape you need. Remember that the plate is reinforcing the damage and once its got fibreglass on the inside, it will dry and be solid as a rock. Then dress the outside with some decent body filler [Plastic padding PP100 is good, albeit expensive] and sand it down with some 80 grit for initial shape and finish off with finer grade papers until the repair is the correct shape and then prime/paint it. Use a rubber sanding block if you can, car body factors sell them for a few quid and they are well worth their cost and will make your life easier.
Dont forget to put some protection onto the rest of the bodywork next to where you are working as fibreglass resin is not forgiving and will ruin paint & trim. Oh, and wear a decent face mask for the dust, plus gloves, etc.
Lastly, do check before you start that you will have enough clearance between the inside of the repair and the original roof or you might have issues when refitting the seal, etc. Dont go mad with the fibreglass, basically.
Let's have a few pics of it once it's all done.
