extension with engineering calculations plan

Hello,
I am looking for someone who can make a house extension engineering plan. The local authorities have approved the extension and are requiring an engineering and building plan.
Main tasks:
It should be clearly shown how the reconstruction should be attached to the main building, including the roof.
Calculation of the load on the foundation is required; the foundation should be strip.
The main house is built simply: plasterboard inside, 100mm timber frame, insulation inside, brick cladding outside, all plastered. But I plan to do it a little differently, and this should be shown on the plan in any way. My idea is:
Layered structure like this:
Interior: Gypsum board
Per 110 Insulation between the timbers
Membranes on both sides
Exterior: Gypsum board (special windproof type)
Another layer of 50 EPS insulation on top
The same plaster finish
The distance between the timbers of the racks must be suitable for convenient installation of plasterboard (600 or something)

Important thing is to design the wooden structure so I can build it myself.
I plan to use the main attic and the extension attic as storage space, so I need to maximize the space in the extension attic. That means keeping all the load-bearing roof structures as far away as possible to increase the space.
It is also necessary to indicate on the plan where the water from the extension will flow (drainage).
I’ll send you photos of the house, the main attic, the approved plan
The construction of the extension should be done according to the principle of a frame Canadian house. A very important element is the explanation of how exactly to attach the structure to the main house and to emphasize that the facade of the house will be made of the same materials as the main and neighboring buildings.
Any questions — the more, the better — are only welcomed in order to avoid any alterations and misunderstandings.
Some chenges in aproval plan:
I need to make changes to the location of the windows on the second floor and the door on the first floor by removing the small window. I attach pictures with red marks.
The partition on the second floor is also removed. main building roof height is 7811