Well, I decided to see if I could add rooms to the attic, and it worked better than I expected.
What was once a 2 bedroom house is now a 4 bedroom house, suitable for up to 6 sims.
This is part of the attic - a TV area.
Even though the couch is next to the shortened wall, it's pulled out far enough that sims can use it.
This is the new upstairs bathroom. On the left is a shower that you can't see.
This is one of the new attic bedrooms. Everything works as it is now arranged. If you rearrange the room, keep in mind that sims can't walk/stand in the area of the shortened wall to the right.
Another attic bedroom. Everything in this room works too, however if you rearrange, all objects may not be accessible. In this room, the bed must be against the wall, as sims are only able to walk/stand in the middle of this room. I tried putting the bed in the middle of the room, and all the sims can do is flail their arms. ;)
This is one of the 2 original bedrooms on the main floor.
Dining room / home office.
The new attic.
This lot requires every EP, plus Mansion & Garden, Family Fun, Celebration, and IKEA. If you want the neutral roof recolor with the white trim by Neveah223, you'll have to download it here.
The original basegame version of this is available here on MTS, however I plan to upload an improved basegame version with an attic - probably later today or in the next few days.
Sorry, there's tons of cc this time, but I didn't include every recolor of every object.