structural engineer needed- Chester

We have recently had our extension plans approved by CWaC and our builder wants us to supply him with material specifications he should use for the construction. Kel Plamer who did our plans (attached) is not able to help us with the project any further and he advised that we should contact a structural engineer to obtain the material specifications.
As you can see on the attached plans we will need to knock down the existing garage. We do not know the precise nature of the existing foundations , nor do we know the existing floor slab. Considering that we wish to leave some of the existing walls in place an individual concrete pads may be required.