Im getting a mini ramp for my 15th birthday, it is going to be outside so it needs to be surfaced so that it can withstand the elements, what should I use for surfacing the ramp?

you could use wood and just put a huge tarp over it when it rains or something like this should do well
http://www.rampsurface.com/gallery/rad-penn.jpg

i also think this chart will help
http://www.soloramps.com/en/news.asp

Use something like Thompson's water sealer on all exposed wood surfaces.
Skatelite is another option but it is expensive.