That type of interior decor is very popular for the "vacation" homes in N. Wi. Like what was posted here, it's T&G pine, nailed just like you would do flooring (in the tongue), air nailer. Polyurethane finish is a LOT easier to apply before installation. No drywall, just installed directly to the joists after insulating. You'll just face nail and tongue nail the first board and face nail the last one. If any trim is installed in the corners or at the edges, the trim could hide the nail heads. If any pieces have to be butted together on the ends, it's a PITA, but the butts can be T&G'd to keep them even.
Double check the area that you'll be installing the T&G for squareness. Just like doing a roof, cheat a little on each board if necessary to ensure the last board is the same width at both ends.
If any of the studs/joists have high spots, they could be planed down, and any low spots shimmed up. Some installers place a layer of 1/4" or 3/8" blue board insulation under the T&G to help with noise abatement, and to help level out any irregularities.
You'll also want to store the wood indoors for a while to get it acclimated.
