Estimation extending dormer

[festive]

We currently have a dormer extension that looks v similar to this.

We wish to extend it out about 2 metres so it is flush with the guttering of the house (flat roof extension will then provide balcony area.
The dormer is about 3 metres wide. Any ideas approximately what i'd be charged to bring this out 2 metres, with a large appeture in the front to accomodate a 2.5 metre sliding door.

TIA

 

[festive]

Ok a vague estimation would be appreciated. Also would it be possible to extend what's there or rip it out and start from scratch as stated above we would like to extend the dormer out a further 1.5 metres.

TIA