You will need to draw any east-west walls or north-south walls that you want in your program.
The command to draw an east-west wall is like this:
World.placeEWWall(2, 4, 5);
This would draw an east-west wall starting at Street 2 and Avenue 4, with a length of 5.
The command to draw a north-south wall is like this:
World.placeNSWall(1, 2, 3);
This would draw a north-south wall starting at Street 1 and Avenue 2, with a length of 3.
The command to add beepers is like this:
World.placeBeepers(2, 5, 3);
This command would, at Street 2 and Avenue 5, place 3 beepers.
See the screenshot below for an example that includes these commands.