Is there a relationship between labour costs & material costs?

[katymac]

For planning/costing purposes?

In what way? Unsure what you mean

So if labour/workmen will cost say £10,000 for a project then the materials will cost £10k/£25K/40K?

I guess different quality finishes mean that a formulas would be meaningless

I'm afraid there's no formula; there are just too many variables!

If it was a simple task like a man is building a wall, he uses x bricks an hour which cost y pounds. His labour for an hour costs z. If he works for 3 hours costing 3z, what are his materials costs? Yeah, in that crude context it kind of works... but not in any other.

Sometimes an expensive item takes the same amount of labour to install as a cheap one, sometimes things are cheap to buy because they're a pig to fit and you end up paying the difference in labour! There's no one size fits all I'm afraid.

What about stuff like pastering? Or rewiring? Are they more standard?

Kitchens & bathrooms are totally out I'd assume

In construction industry a rough guide is 40% materials, 50% labour and 10% preliminaries (management) type costs

There is no relationship, Item A may be dirt cheap but take many hours to fit where as Item B may be very expensive but be a quick relatively straightforward swap or it may be the reverse. Rewiring so may variables from choice of finish down to the construction of the building.

So if I have guesstimate our labour as £12k (assuming £300 a day) and I have £18k left I should be in the right ballpark

Labour is based on an hourly or day rate whereas the material costs will be just that - what the materials cost. Also if you go high spec the material costs will be higher (obviously).

Windows are one extreme (very expensive but easy to fit) and plastering is the opposite (dirt cheap material but takes ages)
Also the specification therefore price of the windows can vary a lot.
I think you need either a QS or a builder's quote. Or for a rougher idea an architect should be able to help

My dad as a structural engineer & also worked as a building contractor - so previously I have had these facts at my figer tips (or at least at a phonecall/conversation away) but he died last year

I 'know' a lot of stuff but some stuff is just beyond me - I may pull out of a house I am looking at because I just don't know enough about what needs doing to it