It's high time we had a floor in our loft. We've been making due (inadvisably) with 1/2" plywood scraps for the last several months. After chatting with the folks at our local building supply store, I decided on "lodgepole pine" tongue-and-groove boards that are flat on one side, with a chamfer in the other. The material is relatively inexpensive, and it looks good both as the upstairs floor, and the ceiling over the kitchen.
I began by sanding the boards, and then, after much mulling over about whether to stain them a different color than the beams, or try my hand at milk painting them, ended up staining one side to match the rest of the wood in the house.
Tyler is installing them, and with each board that goes up, the difference is astounding. A real ceiling! A real floor! It looks wonderful, and it feels even better to have a sturdy, safe surface underfoot.