Two really nice dios. A lot of potential is shown and you have the right idea making small dios and learning the techniques before tackling anything bigger.
The points made above are sound. The only thing Id add, is to the shelter. If somebody went to the bother to build it .. it would also probably have personal items and something to lay down in or sit on. A few bedrolls and back packs, water cans,log seats,etc would dress it up nicely.
A good article on building dios can be seen here;
A Simple Diorama .
That may give you some ideas and inspiration. If you have any specific questions, just ask!