In designing and building the floor-to-ceiling shelves, I left space in the corners for transition units between the two walls. I'd debated butting the two sections against each other and perhaps crafting some "secret doors" into the hollow columns thus created, but in the end, decided 45-degree corner units would be the best use of space and would allow for additional book storage, photo display, and a place for some of the knick-knacks we've accumulated over the years.
Building the shelves began with the back support uprights; using the table saw, Beth and I cut 45-degree angles on the two sides, such that each upright panel would fit flush into the corner and provide support along the backs of the shelves themselves. I still had the drill template handy for the shelf peg holes (although it didn't line up perfectly left-to-right for the uprights--ah, well), and attaching the back uprights to the walls was fairly easily accomplished with several heavy duty wall anchors. I may eventually put in some really heavy-duty long screws through into the studs, but 6x 100-pound wall anchors should be more than sufficient for the duty--and there's really no way the support can collapse; the shelves, once in place, are wedged by the walls and the side shelving units; the back support is really there as a shelf peg holder.
The shelves were a tricky design; they're irregular hexagons, with a back edge (against the corner support) about 7 inches wide, a front edge of around 14 inches, and then two sets of sides (one set parallel to the shelves, one set parallel to the walls) of something like 11 and 16 inches, respectively.
Still, a table saw makes fairly quick work of this sort of carpentry; the hardest and most time-consuming part actually was attaching the facing strips of moulding to the shelves.
With the corner shelves in place, we've now got even more room to grow our library's collection; I also rearranged one of the main upright units to accommodate an extra shelf of paperbacks, which was dearly needed.
There's still plenty to do in the library; although the baseboards are all back in place, and all the shelves faced now, there's still the matter of the purple ceiling (no, that's not an intentional color choice on our part!) We intend to apply some false tin ceiling tiles for a classical look; it's just a matter of ordering them and doing the layout properly. After that, the crown moulding needs to go in along the tops of the shelves to complete their woodwork.
The closet still has a lot to do; at least with getting the corner units in place, we're able to clean out the stuff piled in the library closet so that I can pull up the carpet there and install bamboo flooring like the rest of the library. After that, we're debating how to finish it off; I'll put the closet door back on temporarily, but we want a fireplace (fake for now; perhaps gas logs in the future), and will put in some brick veneer for a nice hearth look... and perhaps a "secret" compartment behind the edge of the shelves where they meet the closet opening. Oh, and the antique claw-footed chair from my grandmother's house: it needs to be reupholstered; we've got the fabric, wood, and foam, but have not had the time yet.
And we have light fixtures to install; way back before we bought Chateau Papillon and were waiting out the bank for the short sale buy, Home Depot had a sale on chandeliers, so we've got a small one to put in over the library's seating area, and will also need some additional lighting at the other end.
With the corner shelves, though, we're one step closer to finishing the library!