First a couple of general points -- Never pay up front for anything, [ interims and a final , as the job progresses, is how we work ] a decent contractor has credit accounts, and own their own plant/equipment , so no need for anything up front . Check the contractors insurance policy that all decent contractors have.
No cash ,-- cheque or bax to the person you are actually employing .
Be around, and ask what is going on , decent contractors will be happy to explain .
Get a written quote/estimate , with a decent works list of what is to be done, and with what .
Confirm that the job will be all in one go , and that you both agree what is included in the price .[ scaffold, skips , clearing up etc ]
Be happy to pay for genuine extras, or additional works , to the agreed list .
Keep quotes to yourself, [ ' Beat any quote' = cannot price jobs ]
Cheap quotes are often for only 'half ' the job !
See previous work
If one company is 'main contractor' , they are responsible for what they have quoted for , quality , coordination, certification, security , LA inspections etc , and the H&S aspect of the trades they employ , you have one person to deal with.
If 'you' run the job, you are responsible for all of this , and what I call the ---' everything else' or the overlap/ gap between trades -- which is a lot of work . On big building sites the Manager [ was me ] has people running around after contractors to keep it all going forward . You really need to be on site a lot of the time if it is an extensive job .
Trick is to find an experienced professional , careful contractor , who can actually price most of the job you want correctly , Rated people is a good way, take a little time to find the right person.
Peter R. ---- Beamish Const. Services.