Get the FSX SDK, from there the world is your oyster. My first success was adding a nearby WW2 airfield, Wroughton, to FSX. I then added some hangers to make it better. I created the hangers using GMAX that comes with the SDK.
I then came across Google earth, and I realised that there were lots and lots of grass strips near to where I live, so I added them, and after adding each one I'd fly to it.
I then modelled the Shard in London, as it came after FSX was realesed, and I added it to FSX and flew around it.
Eventually I started modelling aircraft. There is nothing nicer than flying your own plane, into an airfield that you've added, and knowing that no one else in the world can do that.
Ok, I am a very experienced software developer, and have some artistic ability which helps, but its not been easy, however it has been challenging and interesting.
