This is very broad, you need to break this down into way smaller chunks, design modules for each part i.e. building and line of sight, pathways and obstacles etc. etc. Maybe follow the following link on where to start - WHERE TO START IN GAME DEVELOPMENT[^]
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Many developers love games and want to build games. But game development is a vast ocean. There are so many aspects to developing a game that it's hard to understand where a game developer should even start. One way to start building a game is by choosing how you will build it. Regardless of whether you're an indie developer or an established game development studio, there are 3 ways you can build a game.