flip down dvd player on roof

That would be tough. The back window is so high and the mirror is so high, that that the DVD player would block the mirror. When it comes standars, like it did in my mother's minivan, it was set up so that the mirror was just low enough that it cleared the screen. it also helped that the van was high enough that the window could provide a good view. But just get some help and use a paper mockup to see if you can get it to work in the prius.