How much for a bedroom extension?

[newcamper]

Current bedroom looks out onto garage roof. If we wanted to extend the bedroom on top of garage roof and install en suite at back of bedroom next to current bathroom, what kind of ball park figure would we be looking at? Never done anything bigger than decorating a bedroom. Thanks.

How many square metres?
As a very very very very rough guess, £1800 per square metre.

You would also have to find out if the garage has sufficient foundations to support another storey.

From recent experience. Whatever quote you get add 30% extra for the hidden things.
I think the estimate of £1800 per square metre is about right but depends on where you are located.

VAT is a big factor. £1800 isn't too far off for a basic finish (no decorating / flooring, plus cost of bathroom fittings etc) PLUS VAT which takes it to £2-2.3k per sqm

Yy to foundations being important. Requirements for single story differ to two story. Also drainage is important as is water in. How far is the ensuite from existing plumbing.

We did a similar ground level extension 2yrs ago, knocked down a garage and rebuilt as a single storey bedroom with ensuite and utility. All in about £18k.
You have to remember to factor in costs such as skips, (we spent over £1000 on skips! Removing foundations!) Replastering and decorating the hallway once we had knocked through, this hadnt occured to either of us untill we actuall did it!
Also look into your planning permission stuff, double storey has rules re boundries etc. Not as simple as just building up. And like someone said the garage may need to come down first as chances are it doesnt have double storey foundations.

Thank you! That's really helpful. I hadn't considered the foundations. I knew the garage roof would need additional support but didn't consider what was underneath. The actual extension would probably be about 12 square metres (wild guess whilst sitting on my sofa trying to picture the width of the room). We only talked about it for the first time today and are thinking a good few years in the future (imagining sharing our bathroom with 2 teens). Thanks.

You will need planning permission. Find an architect to come and look at the place for you.

The en suite would be literally next door to current bathroom so only slight plumbing diversion.

The other option is to install a teeny weeny toilet/shower room under the stairs but I think this will end up more complicated as inbetween 2 reception rooms near the kitchen and in the middle of the house so drainage will be a nightmare.

Garage will almost certainly have to come down and new foundations built.
Factor in: planning permission, architect, structual surveyor, decorator, plumber, builder ...

This is what we are currently doing - new bedroom over garage and orginally that was going to be that.

Our garage was single brick so had to be demolished and rebuilt - in the end we decided as we have plenty of room to the side of the house to add in a study/snug downstairs plus utility room and shift the garage sideways. Only slight issue so far has been that the drains needed moving but that seemed to go relatively straightforward.