When a contractor puts a bid on a project, there is usually a time frame included for completing it. The person who hires the contractor is counting on the project to be done on time. Whether the structure is for your personal use or your business, there isn't any reason why you should have to wait to be able to use it. Contractors should plan ahead to include a time cushion just in case something happens that delays the project a bit. Trying to wait until the deadline to get things done is flirting with disaster.
You count on your home's roof to keep the contents dry when it rains. When this doesn't happen, either the roof is old and needs to be replaced or there are defects in it. If the roof was recently put on and it is leaking, it is time to find out why. Ideally, you will be able to get this done before the rains begin again because there is a lot of damage that can be done to the structure, as well as the things in the home or office.