Just a heads up: I've experienced a significant bug in Skyrim's newest downloadable content that seems to be avoidable.
When you get your plot of land in Hearthfire, you'll be using two major devices: the drafting table and the carpenter's workbench. At the drafting table, you can select blueprints for buildings and wings in your new home. Once you've selected a blueprint, it moves over to the carpenter's workbench, where you can actually piece it together in stages: first you build a door, then a floor, then walls, etc.
After you've built an entryway and a main hall for your manor, you can start selecting optional rooms like a library or kitchen. Each set of rooms is attached to a wing of the house -- you can only build bedrooms in the west wing, for example -- but you can only start planning out one room per wing at a time.
This is where the problems start. If you pick a plan from the west wing, start building parts of it over at the workbench, and then select another plan from the west wing at the drafting table, everything goes wonky. You can lose progress and even deny yourself access to entire rooms. (One of my blueprints disappeared entirely, and I can't get it back.)
So what's the solution? Build one thing at a time. Don't pick multiple blueprints from the drafting table at once: just select one, finish all of its pieces at the workbench, and then move on to the next plan. Don't get cute and experiment with drafting, or you might lock yourself out of some of the game's content.
I've reached out to Bethesda to inform them of the bug and ask if they have plans to fix it. If you've experienced any other bugs (and know how they can be avoided) link to them here!