The idea of having a garden on the roof of one's house is a cool one. It struck me for the first time when I read an account of India's Narendra Modi's endeavors to install solar grids over the canals of Gujarat, the province of which he is the CM. Installing solar grids over the canals has two additional benefits along with electricity generation. It saves land space, which can be used for other purposes such as agriculture. Secondly, it saves substantial amount of canal water from being evaporated. Projects involving solar energy have great potential in Asian countries like India, Pakistan and other middle eastern countries, which can have very hot climate specially in the summer months. Indeed, when installed on rooftops they could also be beneficial in reducing the indoor ambient temperature of a house or a similar facility. But solar panels are not viably cheap so that everyone can afford them. However, the idea of installing them over canals or on rooftops has additional benefits as discussed above.
A cheap alternative to having solar panels over one's house is to plant a rooftop garden. Obviously they would not generate electricity. However, they will offer at least three other benefits. First of them is, of course, that the gardener would reap his/her own homegrown vegetables. The second is that it will lower the indoor temperature of the house as rooftop plantation would absorb much of the solar heat from allowing it to penetrate in the house. There is a third very crucial benefit too specially for a country like Pakistan. Pakistan is basically an agricultural country. However, much of its agricultural traditions are being ruined for one reason or the other. One of the reasons is population growth itself. A consequence of that is that a substantial amount of arable land that was once used for agriculture is gradually being converted to habitations. Thus, reducing the land that was available for agriculture. Adopting rooftop gardens would revive significant portion of that land for household horticulture. Growing organic vegetables on one's own roof would also be cheap and healthy. There is a fourth benefit too of having an orchard on one's own roof. Developing a rooftop garden can also be a way of testing and honing one's aesthetic sense about gardening.
Rooftop gardening is quite common in western and other Asian countries. It has, however, not been adopted in Pakistan so far. Of the many reasons a common one is that we as Pakistanis are shy of adopting new ideas quickly. Fear of taking initiative is another common cause. Developing rooftop gardens can have many benefits both personally for the owner and the community as a whole. It can also be anticipated that developing rooftop gardens can be much cheaper and would not require much paraphernalia. Here is a good link to useful advice on developing rooftop gardens.