Thank you all - this is helpful. It's all new to me because I haven't embarked on build - still looking for suitable plot, but I have a very god builder/project manager who will use all his trusted people i.e. roofer, electrician, brickies, plumber so they are a known quantity
I'll use an example. Spirit Energy are a recommended renewables supplier. I want to purchase Sigenergy Battery and Viridian in roof panels. Last YouTube video I saw they had their warehouse stocked with Sigenergy as they recommend it and probably Viridian panels too. I can obviously look to but the components myself and get best discount but truth be told they probably got a much better deal buying in bulk. Would they divulge those material costs to me on a final invoice or would they just roll ito all up into the final supply and fit invoice, which as discussed for a new build wouldn't have VAT on top?
I guess my thoughts are if the project manager wants to use his tradesman - let's say brickies as an example, I say to them ok - purchase the materials you need for this job using your best trade outlet and discount but ask them to put the invoice in my name and address and I pay for it at that time so I can see exactly the units cost - yes I appreciate there a wait to reclaim at vat at the end. Then their second invoice if so the supply/labour bill so I can see the cost for each tradesman
Perhaps I'm overthinking it - as Jack rightly says you'll have an idea of the costs and of course I don't want to upset the tradesmen - important to keep them sweet