if you don't have any rocks on your 'inventory', then you should quit 'cause you can't build anything. but you could build a tree plantation (20 stone). also you can buy forests in 'decorations'. but if you do buy forests (20 wood), you should make sure they are on the 'cut down and regrow' setting so you can keep the forest alive for more wood. i usually protect a few forests at the beginning so i can change the setting if I have no more forests or plantations left for some reason.