Make whatever you want. Tap the white bar above the plants button to see more things to build with. If it is not letting you build something, it is because scratch has run out of memory and you will have to clear the screen or press the green flag. This project works better on mobile devices. I will be adding more materials to build with every once in a while, so make sure to check in every so often.
Credit goes to the sandbox game that gave me the idea to make this ( I don't know what it's called, but I'm guessing it is just called sandbox.)