See inside
I created a custom block that will allow you to create a grid, but I will let you figure out how to get objects on there... Hint: You need to get the cursor to land on a tile accurately, instead of guessing with "move [x]" or "move [y]" blocks, try to figure out how it can land exactly on a spot of the grid. Once you can do that, I'm sure you will be able to place buildings.
