Depending on the property (and the budget), both options have their merits. A big loft space can be more easily converted to a room but often the structure or space isn't sufficient and an dormer or extension is needed. This can offer a whole new floor to the building and with some imagination you can transform the property completely. www.pwjarchitects.com

Thanks Jonathan – a really helpful response. If you don't mind, here are my thoughts on your points: “I think that eventually at least 2 sisters (possibly all three girls) will move to this floor so you might want to make the shower room just a little larger to accommodate all the products they will eventually ‘need’.” That’s the plan – we’re aiming to move two daughters up there for now, and we’ll see how it goes. Good point on the shower room – would you suggest enlarging it by shifting the wall between the shower room and Bedroom 4? I still need to think about the interior layout of the shower room. “You might want to consider the front bedroom and where you would put furniture – probably moving the doors to the loft space.” I’ve been thinking about this. Here’s how I imagine the furniture layout (still need to add smaller pieces like a desk): I liked your original suggestion of placing the bed on the sloped side – I’m picturing eaves doors on either side of the double bed. “Also the roof windows in there seem ginormous.” That was intentional! I asked for the largest possible windows, ideally using coupled flashing (with either an 18mm or 100mm gap) to maximise head height around the bed (like this). I’m also hoping to minimise the central pillar between them to help the head height and to allow the headboard to go against the vertical wall below the window. Do you think that’s too much? “And if you have a Velux above the stairs consider getting an electrically opening one to help heat escape on hot days.” Thanks – I’ll look into this. Thanks again – Appreciate your input!

You don’t have to close off the second space unless you want it to count as a formal bedroom on the plans or for Building Control to treat it as a separate habitable room. Building Control mainly cares about safe escape routes, fire protection, and the staircase layout. As long as the main bedroom space is properly enclosed where required for fire safety, the rest of the loft can stay open if it is being used as a landing, storage area, or general open space. Many people with smaller houses keep part of the loft open to avoid awkward stair designs or losing headroom. The key thing is that the enclosed bedroom must meet the rules on fire doors, insulation, and escape windows. The open area usually just has to meet the general structural and insulation requirements. Your builder or architect can confirm the exact layout, but you usually do not have to redesign everything just to close off that second space unless you specifically want two separate rooms.

Yes, it's called a hip to gable conversation