You have what appears to be the makings of a very nice '28 Blindback - a very nice body style in my opinion. Also, just my opinion, it would be a mistake to consider any sort of metal fabricated roof as opposed to the original design. As Terry stated above, if it were me, I would also take the time to consider replacing all of the wood that showed any sign of compromise, since there is too much involved to take short-cuts in rebuilding one of these wood-framed bodies. For that reason if no other, I think that it would be a mistake to try to fabricate an alternative roof design, since the structural integrity of the car comes from the wood framework and not the metal "skin". Furthermore, it may be more difficult to design an alternative roof line that would have the otherwise graceful lines of the original body without having to make a fairly substantial investment; regardless, the value of the finished car would be severely reduced in that event, again, just my opinion. While any wood framed body is a challenge, the results from taking the time to properly rebuild the framework are well worth the effort. Before you make any decision though, I might encourage you to take the time to make a personal inspection of an actual restored version of this model. In my opinion, the body's grace of line will speak for itself. Best of luck to you regardless of your ultimate decision.
Dick