Once the project plan is developed, the funding secured and commitments given, if you don’t already have one, now might be the appropriate time for you to have a more formal contract with the project leader or whoever is responsible for managing the budget. Contracts are enforceable by law. It is recommended that they be signed, dated and witnessed by representatives of all the parties involved. Your contract will be specific about the time you are expected to commit, what is expected of you during that time - key deliverables - and your remuneration for those services. It may also specify terms of ownership, codes of conduct, confidentiality etc.