How many building component manufacturers (windows, doors, gutters,
etc.)are there in the UK? How many are headquartered in the UK? What
are their overall revenues?

The problem with your question is the etc. Should we include paint,
glue, nails, screws, studs, I beams, elevators, emergency lighting,
landscaping, carpeting, ceiling fans, roofing tar, built in
wallclocks, the heating and airconditioning components, parking lot
asphalt, welding rods, access roads and appropriate off ramps,
electrical wiring, commodes, blinds, curtains, telephone wiring,
thermal insulation? When, if ever, should we include labor costs?
Guessing you want to include about half of these items and thousands
of similar items, there are 200 manufacturers in the UK main islands
(not counting Canada, Australia, etc) (not counting importers who
repackage items made in other countries, wholesalers and distributors)
(Not counting manufacturers that gross less than $100,000 Euro dollars
per year from the building construction industry) The total gross of
the 200 manufacturers is about 100 billion Euro dollars. Adding mark
ups by numerous middle men including the contractors, and sub
contractors several hundred billion Euro dollars. This, of course, is
a wild guess and incudes private one story homes and major
renovations, but not minor renovations, utility sheds, animal coops,
dog houses and construction by children. 80% of the smaller
manufacturers are Headquarted in the UK, but few of the biggest
manufacturers are headquarterd in the UK.   Neil

Good question, difficult to answer in a phrase. Ideally, I would like
a census of the companies that make discrete building products that
would are branded and are attribute-sensitive (i.e., not commodities
and not low-value items). For example, windows, doors, toilets, sinks,
roof tiles, ceramic tiles, draining components, HVAC units, etc. are
candidates. Nails, wiring, welding rods and other low-value and/or
bulk and/or commodity items are not candidates. I don't need the labor
component, just ane stimate of the manufacturer's as-sold revenues.