Again, this sounds simple but should be given careful consideration. Be wary about including future income. A delay in your tax refund or legal settlement, for example, could bring your project to a screeching halt, with potentially disastrous legal and financial consequences if that money was a vital part of your construction fund. Leave yourself some breathing room, too. Keep in mind that it's difficult to refinance in mid-construction.
Banks are loathe to loan money on a home that's unfinished.
The next step is to make a wish list. This is everything that you would, ideally, like your finished project to include. For example, even if your main objective is to update the kitchen and add a family room, you may also wish to replace all your existing windows and enlarge your deck. Include everything, even if you suspect it may not be feasible. This will help to ensure that you don't forego something unnecessarily.