Kitchen Renovation

Ballymoney

I wondered if I could get the opinion of some more experienced folk on the what you think the below renovation work would come to. Its a full kitchen renovation in a room currently 5.7m x 3.7m.

1. Remove current kitchen
2. The current kitchen was extended by previous owners but a large amount of the previous external wall still exists acting as a barrier between old and new ends of the room. I’d like to replace the existing RSJ (2m) with one spanning entire width of room (3.7m) so I can remove all of the old external wall.
3. Extend out by a further 1.2m so room measures 6.9 x 3.7
4. Remove existing sloped roof (3.5m x 3.7m with flat ceiling) and replace with new sloped roof to accommodate extension (4.7m x 3.7m) and vaulted ceiling & velux windows.

Electrics, plumbing, bifolds, plastering etc will all be added but any advice on just the structural work would be greatly received, thank you.