Insted of making a whole new game, why don't you just design a house level for Blockland?
Whole lot easier. It's pretty hard to make a 2D game, let alone a 3D game. And just setting up a server and getting networking right is going to be impossible for you if you are starting from scratch. I would start small and make a "Hello World" program, and slowly work your way up. But even before you do that, plot out your whole idea on paper. Write down as much as you can like gameplay mechanics, possible bugs/bug fixes, game engine, price (It's almost impossible to make a game totally for free), draw pictures of what the charaters/objects will look like, etc. I know all of these things and I don't even program! My friend and I make games (He does most of the work, I make the art and debug when he sends me a beta but we both design it).
Here is a link to his website. It hasen't be updated in about a year, but I'll post a couple of links to his other games.
Here is a link to Drill Garanz. If I can get a copy of his latest game, I'll post it, but I've only played it at his house.
