We've had an unfinished bookcase in our master bedroom since... I'm not even going to say how long I've put off this project! It needed a picture frame casing and trim paint to match the rest of the bedroom.
After a trip to OWL Lumber for some casing, I went to +Pumping Station One to cut and assemble the frame. I used square head trim screws to help hold it together on the ends with glue. Its a real pain to clamp the ends since you have to deal with 4 corners all at once and the glue coming out the bottom. Other recommendations welcome.
Once I brought the frame home, leveled the bookcase in the opening, and I nailed the frame in to the bookcase side panels.
Two coats of Sherwin Williams ProClassic and 3 day dry time later..