Mr Punter

You should keep your patio level 150mm below DPC to avoid damp issues. Patio level with internal floor level is asking for trouble.

I think coring a hole and installing as per your drawing will be good. I have not seen these before but they look decent.

Any less would be bouncy and not reassuring to walk on. Rafters would need to be 400 as well.

It will be fine if the rainwater connects into a combined drain. I don't know anyone who has ever changed the limestone chippings in the soakaway version.

Cavity barriers and firestopping is often left to "others". They often get left out as nobody really knows what to specify or order or fit. Were they specified and detailed on the architects drawings? Rockwool would be a decent choice for non-vented and Envirograf for intumescent, vented rainscreen applications. I would want detailed spec and drawings, so nothing gets missed on your order or on site.

I really like the XPS backer boards. Lots of thicknesses, lightweight, easy to cut and fix, waterproof. Fix with adhesive foam or screws and washers.

Can you clarify if you intend to extend the existing ground floor, also adding a basement under? Without a floor plan there is a limited amount anyone can suggest. I think that having a measured survey of the existing building and plot would be a good start. Have it include a section through the house / plot, neighbouring properties, front and rear elevations. Budget £1,200. Make sure you own the rights to use the plans.

If the rooflights are toughened and laminated the requirement for balustrade may be reduced anyway. Don't forget access for cleaning with all that glass.

Well that is good to hear. My experience has been that they have been difficult to deal with, I could not get the online part to work. They often want to send out a salesperson but I had issues getting prices. I would like to use them, as they have a branch near me but they are not easy to do business with.

A shame because I have found Howdens arseholes to deal with and have bought about a dozen from DIY kitchens.

If you have a 50mm layer of rockwool compressed under the sheets it helps a lot, but you would need to take the sheets off and refit.

Where we are, if you don't have the right ducting the DNO (UKPN) won't run the cable. They will tell you what they need. Just re read and I see this is your side of the meter, so 100mm rigid duct will be OK.

The bricks you have shown do not look standard size of 215 x 100 x 65 they look longer or not as high. There are quite a few foreign bricks non-standard sizes. The proper lime mortar looks good. I would be tempted to get local clay stock bricks as anything imported can have a fair lead time and delivery charges.

Agree with @BotusBuild. Aco drain will work well here. Hopefully there is somewhere you could connect it to at the end.

Tell them you can set the test up and they can come and witness it. I would not want to spend £400 just because someone is being a numpty. Part of what you pay for is inspections.