I haven’t done, but I have certainly seen pictures of attic rooms shown on the forum. To avoid noise transfer you need to apply appropriate soundproofing in the floor and walls/ceiling. The most efficient common heat insulation material, the Kingspan type rigid polyurethane foam board, is good for thermal insulation of sleeping roofs, but is poor at sound insulation. For that much better would be high density mineral wool slabs (not the lightweight mineral wool usually sold in rolls for loft insulation), though from the thermal insulation point of view it would need to be some 50% thicker than insulation.
What sort of loft room is it? If it’s a conversion the floor timbers will have been very flimsy compared to proper joists as they will only have been designed to hold up the ceiling below. A proper conversion would probably have uprated them, but if this hasn’t been done well you may find that the floor has a lot of bounce in it, giving poor acoustics and poor sound insulation for the bedrooms.
I don’t think sloping ceilings are likely to be a problem. If anything the likelihood of room nodes could be reduced.
I don’t know, I’m only at the stage where I’m trying to weigh up all the options of where my listening room will be in my next house. Planning to move in the new year
be aware loft conversion building regs have changed significantly over the years and now involve a complete removal of roof and the ceilings beneath to upgrade to proper fire protection. Older conversions can be pretty shoddy plus cold in winter and hot in summer….
My listening room is upstairs in the roof-space of our new-ish self-build. It’s a mono-pitch roof, 2.4 m ceiling height at one side and 1.5m at the other. The room is around 6mx6m. I’ve never felt the sloping roof caused any sound quality issues. There are substantial floor joists with mineral wool insulation but sound still transfers to the room below. My wife originally had her home office in the room below but has now moved two rooms along and there is very little sound transfer now .
I had a loft listening room with sloping ceilings and had no problems at all. I moved home a few years later and built a brick listening room in my garden.