Mr Punter

Ask the SE. It is their job to specify correctly.

Crushed concrete / brick will be OK but not any old crap with plaster, wood, rubbish mixed in.

A friend was doing and agricultural shed and he went for timber frame 8 x 2s as you only need to nudge blockwork with a telehandler and it collapses whereas timber frame bounces back if it is constructed correctly.

The 22mm is annoying but is only 1mm per metre. With the sub structure stuff it will be possible to rectify but I would point out that I expect it built as per drawings. Better to let him know as he progresses than after he has finished. Check the drawings each day and go through with him in the morning where you think he might mess up.

I am hot on avoiding on high risk / severe consequence incidents, so falls from height, buried in a trench, brick on your head, crushed by materials / machine etc.

Timber frame stick built with mineral wool insulation and 18mm OSB internal sheathing. External cladding of your choice. Strong, simple, lightweight and cost effective. Pitched roof would be my preference.

We have used the Kytun Ali trims on natural slate. No issues with slate / slate and a half.

I have not used this one but have been able to get an email address to send Build Zone documents in the past, as at the time their portal had file size limits. Call them and ask what they suggest.

Have you been in touch with the tilers, or was this DIY? I have not used fix-a-floor but there should not be problems with the tiles over such a large area. If it were me I would do a small area and monitor before taking on the whole floor.

You did well to ditch the green roof. Unless the planners included a condition that the house could not be occupied until you have written approval for the roof as built there should not be an issue.

If it looks OK then it is OK. I have a property where the floor slopes 50mm over 1200mm. You only really notice when you look at the plinth.

I understand that Sweet Chestnut is a good durable UK timber.

If you are on clay soil you would need to excavate a vast amount and backfill with the granular permeable base material. You may need to go down half a metre from the finish level. I have laid permeable paving on a fairly thin bed of granite chippings on chalk subgrade and it drains very well.

The boreholes should not be too costly. If they are good designers they may use the information from the geotechnical report for a more cost effective solution for the pool.

Another vote for adding more battens. Just remove any that really mess up your gauge. The extra battens will strengthen the roof a bit. Could you get different shingles to work?