Suppose you cannot use players' or DM apartments. Where would you play a whole campaign ? For the very nature of roleplaying, pubs and public libraries are not appropriate. Any proposals ?
Actually libraries and pubs are both good choices. Our local historical mini's club routinely uses the library and The Escapist sponsors Terra Libris, a project to play RPGs in libraries.
A local group plays in a 24/7 McDonalds on Friday. We have a local university sponsored club.
I've played quite a bit in coffee shops. Just keep buying refills and the occasional pastry. Hell, I suspect we spent more per hour than the local college students who were studying.
Malls and some big box stores have activity rooms. These are easier to get as a club, however.
If you have a good gaming store, they may be willing to host your gaming group, especially if you are good customers of the store. It depends on their space--but I've managed a Saturday game at a local game store for several months. This is usually a better option if your game is open to new players, but it can be useful in all cases.
Libraries and public universities often have reservable private spaces that members of the community can use.
Pubs and restaurants similarly often have "private rooms," if you are going to be spending money on food and drink and not just freeloading.
Many privately owned public spaces (malls, etc.) will tolerate you depending on your behavior, especially if you pick a place and/or time that they're not very busy.
Many game stores have some gaming space, though I consider this to be an absolute last option.
I played in a game hosted in the food court at the Dobie Mall in Austin - it's a nearly-abandoned mall near campus, so we certainly weren't disturbing anyone.
I also helped organize a local RPGA club in Memphis, where we used libraries and game stores to host game days.
I've adapted my attic for a gameroom and it served us well except days with temperature over 30 and below 15 grades Celsius. I totally recommend that.
If still at school you can ask for an unused cellar or attic as well.
For older people pubs with lots of small rooms could be promising :) You can set reservation on a table in a tiny room where you'd not be disturbed nor disturb other people [rpg players can be disturbing to watch :P]