That depends on what you negotiate with the contractor. For example, it would not be fair to expect the contractor to buy all the materials needed, without paying for the materials in advance. Then there should be another percentage paid at start-up; another at a specified point of completion, and the rest at the end. The percentages could vary quite a bit between one contractor and another. Do get at least two, preferably three bids. And do have some very specific ideas about what you would like to have done, before you ask for bids. A competent contractor will usually make suggestions based on your ideas. It should be an inter-active, friendly business relationship. If you and the contractor start out not liking one another, that probably won't change, so it's best to choose someone else. Neither of you will benefit if you decide to make major changes in the project, or nitpick all the way through.