I think my architect has cocked up

[Howdidthathappen1]

Hi - I'll try and keep this consise but would really appreciate any advice

Had architect draw up plans for amongst other things a large dormer on the side of our existing loft conversion to our bungalow. On the CAD he's put a disclaimer saying something about not able to measure so has made assumptions.
Turns out his measurements are so far out I'm losing a third of proposed useable space upstairs and feel massively cheated. It's because of the slope angle of the roof - in my head there shouldn't be an excuse to estimate that as it's easily seen.
The work is well underway - the new structure built so the size that the existing roof allows.
I've got an emergency visit from him tomorrow and not sure how to tackle it. From what my builder has explained and I've seen it just can't be rejigged within planning control.

Do I have any come back? I'm spending nearly 100k to gain literally a cupboard and still have a cramped bathroom with what we're left with.

(we were away for 2 weeks until yesterday).

I think that this is another way you have been naiive, OP. Never, ever, go away and leave everything to your builder to handle/decide. Be there, on the spot. It's a bore, but the only way to keep some control.

When we had work done on our house, the only bit I didn't like was done when I wasn't there that day and builders made their own decision about it.

Anyway OP, it's good that you're being stoic, in ten years' time you'll look back and it won't be so important.

Thanks to all that have replied - I have appreciated all advice
So the architect is a chartered architect - just not a v good one it turns out. He claims that he couldnt have know about the angles exactly as the roof space we're going into was sealed so couldn't be viewed.
So between him, the builder and us we've come up with how to create a feeling of more space - obviously without actually having more space. They're going to do technical things with beams and rafters to allow space for the 1700 shower.
Tbh we can't change what's there and the restrictions put on us by planning. It all feels like our hands are tied.
Never again!!!

So glad it worked out for you! (or sort of worked out, at least) Like PP said, in a few years time you will have forgotten all about it.

Are you going to complain about the architect?

@Howdidthathappen1 I think your architect was remiss in not explaining the limitations to you. Most architects will know how a roof is constructed! There are various options but age of house is the first clue. Do you have no loft at all? I’m glad you are getting something that is nearer to what you want but it’s difficult to see how an accurate design could ever be drawn up without knowing the roof structure. It’s absolutely vital.