Creating a game which runs as a web application requires
- Game design - design of the rules and content of the game
- Application design - how is the application going to work? How will you prevent cheating?
Neither of these things is straightforward.
I recommend that you THINK about the design of the game - how it's going to work - turns, ticks, resource allocation, movement points etc. And think about the thematic design of the game - the scenario, types of character, objectives etc
Think about the design of the application from a technical standpoint as well
- If it's tick based, are you going to use "cron" - what would be required to be done on each tick?
- If stuff is happening interactively on the web, how are you going to make it fair from the point of view of regular vs occasional players etc?
- Are you going to use (e.g.) AJAX or Javascript
You will also require graphics and text design.
Mark