An example of what your house might look like in an urban area, if you are poor. You would pick up scraps from the dump and make a home. You could put tire gardens on your roof to help keep it from blowing away.

This is a method of urban gardening that is a light weight solution, it is called a sock and can garden. Plants need 4 things to grow Air, Water, Light and.....No not soil, but nutrients. So the way the sock and can garden works is you take old pop cans and old socks and make holes in the cans and stuff the socks with the cans and place them in an old container. Then you can plant plugs (plants that have been started in a tray) of some sort of plant in the rows of cans and mulch them, you must water with some sort of fertilized water to feed the plants and the socks act as a wicking material to spread the nutrients around to the plants and eventually the roots grow into the socks and cans and the plants grow (as seen below). As you can see in the picture above there is also an old pot with holes in it in the middle so you can keep an eye on the water level in the container. This container is very light weight.

Another small container garden you can make is with the use of an old tire. Cut off the top and line the bottom with plastic and then invert the top part that you cut off and place it on top of the plastic so that  it hold the plastic in place. You can fill with dirt, compost, some cans and then dirt etc. depending on how much weight your roof, balcony etc. can hold. Then plant something in it and you have a  source of vegetables growing at your urban home.

Here you can see some examples of tire gardens and other discarded containers used to hold dirt and plants.