When renovating our house we bought new room doors. Though they took weeks to be delivered and we already lived in that house without room doors (also no door for the bathroom).

But we had loads of big cardboard pieces from furniture, so I used them and a lot of glue to build temporary doors. I added handles and used screws to fix them in the frame (I mean the big wooden beams, that are holding the actual nice doorframe in the wall).

They mostly worked surprisingly well, holding in the frame by friction from cardboard blocks, that I glued to them. Though they opened everytime, we had an open outside door, that caught some wind