Well, My suggestion is to Google "php tutorial". It's a relatively simple language - for what you are looking for, you could probably learn enough to write it within 30 minutes. The trick will be to just grab values for things like uptime from the appropriate CLI apps. System() should let you do this.
I promise, I taught myself a smattering of php in a half-hour. If you have any other programming experience, this should be a breeze, and if you wrote it yourself, it'll be more maintainable to you.
If you'd just rather not, google "php uptime" for a wide variety, and here's a script for load: