I would start by figuring out what you want this game to be. Write out some basic goals before jumping in.
After you've got a good idea of what you want it to look like, pick a direction. Separate the game into much smaller tasks and pick one to tackle.
I'm actually working on a top-down tile-based RPG right now and I chose to create the world and a player just so that I could start moving around and testing collision, etc. A couple hours after I started I've got a dude running around multiple levels. Using placeholders for your art will speed up the process quite a bit.
For my maps, I'm just using basic arrays to hold integers. Each one represents a different type of tile to draw to the screen. Also, when you move off the screen to the next area, the map get's loaded as the current level and redrawn.
Right now my game is super simple and easy to get up and running. You can check out the source on my github page
and I wrote about the steps I took to get the map up and running on my blog
TL;DR - Break your ideas down into small bite-sized chunks and pick a direction to go in. You can find more help online for small topics rather than a very large topic like tile-based games.
Now go out there and make another awesome RPG. The world doesn't have nearly enough of them!