I saw this nice attic tutorial on tiktok.
https://www.tiktok.com/@taliexottv/video/6988526668205903110
The only issue with attics I see is that they are dependent oh height of roof. In real life people would hunch over or crawl on their knees to reach lower spaces, but I don't really see the sims doing this. I've created livable attic spaces with the mansard type roofs before and they work fine because they are basically rooms, but with the regular roofs there's usually not enough space to create an attic and if you want more attic space you need to create a massive roof and house.