I'm sure everyone here is decent at coding, but on the art side of things, that's where things start getting fishy. Well I came across this site http://www.vgmaps.com/Atlas/PSX/index.htm#A
It has a few commercial maps from some popular platformers of old. You can not use these in your own game....YOU CAN NOT USE THESE IN YOUR GAME. I do think they are useful in seeing how to create a successful map, and where to go from there. You could also get some ideas how to build your tiles to yield some amazing results such those displayed within the maps, cheers!