I agree totally 100% with you Bob.
Having worked in the building trades myself and even my plastics business was supplying to the building trades among others.
My company was originally setup with a structural engineers practice (Sloma partnership which later became Allan McEwan associates).
I was the Void Formers Ltd side of the practice, anyone who has done any piling will know of my patented products (heavesleeve and Formavoid).
I was well known n the industry as the tube man, tube technology our slogan.
I have kept samples of concrete and been expert witness for some and most of the big building companies.
I have seen some tricks and disasters in my career and wouldn't like to see it happen to a member of our group.
We had little knowledge to go on and I wasn't looking for an argument but pointing out things a DIYer might not know.
I have seen serving hatches put in toilets, houses literally sunk into the ground to chimney pot level overnight, listed buildings knocked down, heritage buildings converted.
All because the DIYer and builder has not known or researched what he is doing, all these things had to be corrected and somebody has to pay for the correction.
If I didn't know what I was doing then £400 will have been money well spent on your services.
I have piled some buildings to the tune of more expense than the building was worth due to incompetence.
Frenchay Hospital in Bristol now stands on my foundations with some piles going a depth of 150 metres because it was built over a Victorian rubbish dump.
I made sleeves for the QE2 bridge to correct failed structural works, it is not only the roof that needs to be considered but think about the foundations to.
None of this may be relevant in Rays case but y other point was this is a public forum and anyone else reading it may think it is a simple process and could come a cropper from advise given.
My advise is still, if you dn't know then don't attempt any structural work, get someone who knows to do the work.
My word I can rabbit init?