Job description

We need plans to be drawn to accurately map out a single storey rear extension, to be passed onto builders. We require that they be suitable for submission to the council for planning permission (if required) and to meet building regulations. Guidance through this process is sought.
We have a fairly clear vision of what we wish to achieve upon completion of the project. The existing kitchen/lounge area is to be further extended, creating a larger open plan kitchen/diner area. A 6 panel bi-folding door system will be installed out to the garden. The newly extended area will be covered by a pitched tiled roof with 3/4 velux skylights. The extension will run the entire width of the house. With it being open plan, I would assume steels will be required to support the existing back wall of the house when it is taken away. Plans will need to include the necessary structural calculations to inform the builders.