You need to know the rates, its not like Art Department, there are no deals from carpenters and painters, which is not always a bad thing for you. The fact that a stage hand on anything other than weekly film rates, will charge £240 per 8 hour day, means, you, as his or her supervisor should be paid considerably more for your longer day and greater responsibility. It also forces your client to be rational, no matter how much we are all supposed to love what we do, if they ask too much, too late, and to randomly, they will have to pay for it at some point. Formal rates in construction are great leverage for your art department crew to also receive a little by way of reasonable working conditions and rights. They can resent constructions lack of team spirit but it does emphasise that this is a professional enterprise and that only helps everyone’s position. The biggest risk in budgeting a build is underestimating the build labour. Overtime is a killer, so get the construction manager to price the job and he or she will keep to it, put in 20% as a margin and you will find, you use it on mistakes and miscommunications. Allow resources for extra transport, as there will always be something asked for late, that needs to be bought.