Hi learner and welcome,
Changing a roof is no small job, it is the backbone of the car and when u cut it off all pillars will sag inwards and need supporting, then u have the lead joins and the poisonous dust u grind to deal with.

without seeing it i think it would be easier to panel-beat the areas in need of work. especially if u r putting a vinyl roof back on.

I worked at Australian Motors Mitsubishi panel shop when the first magnas were new and there were heaps of faults from the factory on the first cars and a common one was the roof, but it was easier to fix the roofs on the car than to replace.

another tip is i had a vinyl roof on a 76 fairlane marquis with cream vinyl roof. I used armor all which looked ok but needed doing often, then learned of using floor wax instead, it looks just beautiful and stays that way for at least a year.