First, let me say, if you paid to have it built then it should be the responsibility of those paid to do it correctly. Shed or house it should not leak. Good building practices should always be used.Now, with that off my chest, let's go on. I have built sheds, houses and larger structures and none have leaked unless a mistake was made somewhere. When dealing with water first look up. Follow the path that water would take from roof to ground. Any place that looks like water might find it's way inside, apply silicone chalking. It's a simple fix , but one that works in most cases. Since you have teenage boys, let them have a crack at this. It will be good experience for them.