I am sure that this has been asked loads of times but here goes. Planning is very likely to be granted for a house on our plot. We are looking at the next steps in terms of whether to build ourselves or sell the plot. I want to get a fairly accurate idea of cost of excavation, retaining walls, foundations, and the build itself so get an idea of how much finance we need to raise to build. What are the best ways to do this, costing from builders, QS, online QS?