Ok, so the pros may possibly disagree with me, but as a dyi'er, this is how it do the floor, trim, paint thing...
1) remove all baseboards, etc, and sand, stain and finish floor.
2) wait until the end of time for the floor to dry. ok, it's not really that long, but i try to give it like a week. and since doing a whole room doesn't happen overnight for me, it may be the next weekend til i get back, so it's ok. but the point is this, when you read the directions on whatever you use to finish the floor (i like polyurethane) it will usually say so long til another coat (if needed) so long til light traffic, so long till moving furnitue back, and so long til "done." lol well... i live in a humid area, and weather can effect times, so i just add a couples days because...
3) i now install plastic sheet over that entire floor, masking up a bit from the floor, where the baseboards will cover
4) mask over doors and windows
5) i was going to say spray ceiling then walls, but you said roll, so paint the walls...
6) then paint the trim... BEFORE i install it with finishing nails (note, plastic still on floor) actually, i paint it early on so it is nice and dry by this point, but you get the idea
7) touch up trim in place
8) gently pull back plastic, install previously painted baseboards, and touch up
roll plastic all toward middle of room and remove
now, you may get a small drop of paint on that floor, BUT, if you see it fall, and you are quick, a damp rag will take it right back up. note i said "touch up trim" this is mainly filling the finishing nail holes, then a quick swip of paint to hide that. don't overbrush, or it will look like crap.
like i said, the pros probably have ways they like better. but sanding a floor without trashing your baseboards can be tough to do (and still getting all the edges is a royal pain in the a**.) and then trying to paint those baseboards in place??? yuk. I like nice looking work, but way too tedious to do well.