Pay the builder. Get the cost of materials agreed on up front.

I take it the triangular window is under the roof eaves or something, and not in a square wall?

Very nice.

Obviously the problem with a pointy window is that it's impossible to put a lintel above it. Do you know if that's a supporting wall? You could have problems if it is. Given the pitch of the roof I'd have assumed the supporting walls were the ones running the other way, but you appear to have a roof with a parallel pitch the other end of the house, so it's hard to tell.

Obviously the problem with a pointy window is that it's impossible to put a lintel above it.

Nah, you just have an arched lintel.

Yeah, a big-ass apex lintel is what you want there. If you go online and search Keystone or IG Lintels, you can fill in a form with all the critical dimensions to get an idea of what the cost will be.

The main way we save the client money when building is to get away from the products the Architect specifies and find more economic alternatives. Names you need to look out for, and try to find alternatives to, are Catnic lintels, Kingspan insulation and Gyproc plasterboard. You'll pay price the rate per m2 for Kingspan insulation as you will for Celotex or Xtrathem for exactly the same specification.

I don't know your financial situation but assuming you don't have a bottomless pit of cash, it's also advisable to pick a bathroom to compromise on at this stage. In our house, our en-suite is the highest spec, followed by the family bathroom, followed by the upstairs shower room. The complete shower, plus WC and basin costs us £310. I've set a budget of £10/m2 for field tiles for the walls, with a little extra for a feature band or mosaic in the shower, and it'll have vinyl on the floor. It'll look absolutely fine and pristine and new but the money we save there will go towards my sanctuary downstairs!

The most important thing you can do as a client is get your brief and performance spec finalised. You (your designer) need to specify absolutely everything, from the level of solar control you want for your glass, to the type of sub-floor you need. The builder is pricing to win the job, he will not voluntarily price things he knows he can leave out or reduce the spec of, and that leaves you open to lots of extra costs once the work begins.

If you'd like, I could take a look over the plans and suggest what things you should consider now and what you should be looking at. It's so easy to blow your budget before you even get as far as finishes.

Bit of background, I'm a quantity surveyor working for a contractor so I'm all about reducing costs and noticing the things the architect has left out!

This the proposal, (rear of house) we would have no ceiling as such in the bedroom just use all the gable end space

Bold move making a big hole on a Friday