Help with a single skin issue

[Mybloodycat]

I saw a house I would like to buy. It has an “office” which I had planned to use as a bedroom, but on inspection it’s a single skin room, basically it’s an outbuilding they’ve done the minimum to and put no radiator in, so can’t be slept in.

What are the options with it? And vague costs? It’s 11’6 x 9’6 so not massive, and it has a weird hallway that runs alongside it to a back door.

I need a 4th bedroom but I’m rubbish at knowing what to do.

Without putting in an extension, can this be made into a bedroom? How would I do it??

I have attached the floor plan, the room is the office with the weird hall next to it

To meet current building regs you may well have to pull it down & start again. It's practically at that state anyway. The floor and walls will need insulating, you'll need electrics and pipework. Whatever roof it has will probably need an upgrade too.

Sometimes retro-fitting is more expensive than building from scratch.

My neighbour has a similar extension on the back of her house. 3 outer walls & a flat roof. It was always bitterly cold. She's just re-built it with celotex on all faces and in the roof.

For a room that size would it be worth the costs to put a proper extension on? Does anyone have any ideas on costs?
I don’t know if it would be a lot of money for no real gain financially in the long run?

Is it the old garage and they've just enclosed what we're previous outside walls to make the corridor?

If so when was it done? Is there any documentation as it's supposed to meet certain standards to be classed as a room.

You can kingspan on the inside but you will lose internal space and will need to redo all skirtings, door frames etc as well as new plasterboard.

Floor would also need to be insulated so what's the headheight and roof construction?

If it's an added extra for the house fine but if it's priced as a four bed I'd steer clear

It’s a 1930 house, no driveway so I think it’s some form of outbuilding, and yes I think they’ve probably enclosed the outside walls.
I’ve not seen any paperwork, but it’s used as a sort of beauty room, with an electric heater.
it’s marketed as an office/study, it’s fairly pricey, I’d certainly look to offer a lot less because I had expected it to have heating in it, but they seem to have just left the exterior as it is and skinned the inside walls!