Yes, you could build all things you want, possible in the Java-version but in the Unity-version it has now become much easier for most players.
FioO A good effect for ruins is to use different kinds of stones which gives a weathered impression. Add a few missing stones and a vine or ivy, to it and the whole thing looks more decayed. Different texture scales on the stones also gives an old effect. For furniture, you can paint over it once or twice with a paint roller to achieve a weathered look.