Indeed, it is best to come up with your own software, for a number of reasons.
1. If you build it yourself (or at least to your exact specification) you will better understand your own site and how it works.
2. If something goes wrong, you will be better placed to fix it. What if someone finds a huge security hole in the 'pre-made' script's code?
3. Get the features you want and nothing you dont want!
4. If you can't afford to get the software done, or don't know how to do it yourself, chances are, you won't be able to do a good job of running a successful file host.