I wanna put down flooring in an attic and it has no flooring whatsoever. All it has is wooden boards and insalation...
screw half inch plywood to the boards and put your flooring on that.
Depends on what kind of flooring you want to put down. Carpet would be the easiest. Nail track around the edge. Roll out underlay. Roll out carpet. Stretch it , cut it , and you are done. Laminate is pretty easy, too Ceramic tile will need an extra layer of plywood to keep it from flexing. Takes a lot of time to lay tile, and can be messy. Lino is probably the most difficult. Best to stick to carpet
Are you making the attic into a conditioned room? You will also need to do the right things for air-sealing and insulating the rafters to be safe and comfortable, and not cause problems in the house. In that case, though, yes you could lay plywood as a subfloor and put most any sort of flooring over that. Watch out that the ceiling joists will be strong enough to support a new floor (and furniture, and you, etc). Or are you just putting done some flooring to store boxes in the attic? Then you can just lay the plywood over the ceiling joists - but first be sure that you have all the insulation you need (or will want) - and if you can see the ceiling joists you don't have enough. So, either way, think about it, and get some good advice.
