The first use is, of course, to harvest all that solar energy that hits the rooftop of the house. Women bring their vegetables, pickles, and fritters to be dried in the sun, and the terrace of a home is often a delight for a small child, with delicious tibits spread out on mats. Some children are also given the job of guarding these self-same tidbits against marauding crows and sparrows, with the promise of a small reward (augmented, of course, by regular samplings!)
The terrace is the place (no longer true in apartments, alas!) where the family's washing is brought up to be dried, by free solar power. Who has not been entranced by the lines of colourful clothes billowing in the sunlight!
Terraces have always been associated with love, which often is carried on under the guise of all the activities above! Those who are caught up with the mundane details of life in the lower floors, often come up to indulge in romance....the young girl spreading out the sarees on the clotheslines often lifts up her eyes to the young man teaching his younger brother to fly a kite...
Unfortunately, the terrace in a building is quite a public space, and other people (epecially children) delight in spoiling the mood of the lovers.
Here's a song with children playing voyeurs..." mottai maadi mottai maadi love jodi love jodi"...terrible lyrics, but the song is fun!
ThanimayilE inimai kANa mudiyumA (Can you find sweetness in loneliness?)
Many Muslim houses also keep their "kabootharkhana" (pigeon nests) on the terraces, and its beautiful to see the birds fluttering up in unison against the morning or the evening sun.
The terraces of old houses have given rise to many romances, and many songs are pictured on terraces. Here's a beautiful song set on a terrace:
Here's a nice cartoon about love-on-the-terrace:
With shamiyanas constructed on them, terraces also used to make a good place for food to be served during family weddings, in the days when weddings were held at home.
I remember, so many of us together, during the Leonid showers a few years ago, or when there were lunar eclipses, gathering with chai and snacks to watch the celestial spectacles...
Even today, in an apartment building, a terrace is often a kind of common space where neighbours can meet and spend a little time together. On a terrace, one is somehow apart from, and above, the cares that oppress one down below. The perspective and the view are different, and it's a good time to enjoy oneself, or introspect....
Given this social history of terraces, it's a pity so many builders just put a lot of water pipes on the terraces of apartment buildings, and completely spoil what could be a great place to gather and socialize. I do love terraces, as an extension of Indian habitation.