I agree with Midnight Spire, just make something small and free to start with if you don't know much about coding. You can also opt to use Rom Hack tools which allow you to modify existing PKMN Roms quite a lot to the extent of basically being able to make your entire own PKMN clone. Needless to say though you can't sell that either because it's copyrighted by Nintendo.
If later on you'd prefer to make your own thing inspired by PKMN you could try GameMaker which has a free version now, although don't go expecting plugins and scripts to be available for each and every thing you want to do on the project.