Hi Brucie
First of establish who is reasponsible for payment, this is
very important especially where builders are concerned.
Once you have established this get a works order number for reference on your invoice.If you don't do this (and they will probably not issue you with one if you don't ask)then when it comes to payment or chasing payment they will delay it as long as possible, probably months, as will say they have no reference to work to.It's an old trick they always use on new contractors
If you have never worked for them before and have no credit/terms and conditions arrangement with them then issue them with a Proforma Invoice.If they will not accept this then it's your call as to whether you want to take a chance and accept the work.
Remember aswell that if the work is for the builders they will deduct tax at source sometimes up to 25% so be prepared for that.It's then up tp you to claim it back from our good friend the Chancellor.
As you have probably gathered by now I have experience working for builders good and bad and have been knocked on several occasions.If you are working for one of the big boys ie Balfour Beaty etc you will be fine as they work to correct procedures if not BEWARE
I hope I havn't frightened you off as this type of work is not only easy but profitable, so long as you get paid.
But you must cover your back.