Bring your fitter with you and purchase the bathroom suite and accessories, so that he can advise you. Don't give the builder the money to buy it, as there's a chance they will use this money to fund another job and drag their heels on yours until they get the cash from another job to go out and buy the suite. I'm not saying all builders would do this, far from it, but this is a way of protecting yourself from those that could potentially. By bringing the fitter with you you may avail of trade discounts they qualify for. Unfortunately I'm speaking from personal experience here!!!