Building a house in the desert with very little material. Basically instead of building the house, dig it up. Add on some self tainting glass roof to benefit from all the sun light, a couple of solar panels in the 'underground' garden, which is obviously at the same level as your house (i.e. underground) and some system to recycle water for a month or so, while waiting for the next delivery by truck.
Would be great in Algeria where there is over 2 million squares kilometers of desert to grab and the state gives you free concessions for 99 years. Could turn into an estate (they give up to 100 square kilometers for free) and start up some hi tech, hi added value products business and ensure enough cash for the whole environmentally friendly thing to work out.
Problems: haven't got a clue on the architecture and technical stuff surrounding such a building project?
Reward: A free Saharan dug up house like this.