Rooftop squatter huts on old Chinese buildings, or tong lau, spread like ant colonies in the 1950s and 60s following the influx of mainland immigrants after the second world war.

'Rooftop squatter huts are a Hong Kong miracle,' said comic artist and animator Stella So Man-yee.

'I'm amazed by the squatter dwellers' ability to accomplish so many things in such a limited space. I'm also impressed by the variety of colours, the multiple layers and rich textures of the huts.'

This month, So and collector Joel Chung Yin-chai published a two-volume collection of their photographs and illustrations of rooftop squatter huts in Cheung Sha Wan and Tai Kok Tsui over the past two years.

The book has a poetic title: Sky City, which is the same title as Hayao Miyazaki's animation Castle in the Sky in Chinese.

'I like the work of Miyazaki. I also find that today it is a luxury for people to live under a blue sky,' said Chung, who has collected old textbooks, toys

and anything that might be considered a sign of its time since the late 1980s.

So said the flowers and plants on the rooftops of tong lau often make them look like 'gardens in the sky'. Most high-rises - residential or commercial - have sealed rooftops.

'This is a sharp contrast. Some people spend millions of dollars on a luxury flat, but what they get is a confined home. The squatter dwellers don't have money, but they can enjoy the sun and fresh air,' said Chung.

The book comprises Polaroid photos and panoramic pictures as well as drawings by So and Chung.

The aim is to provide readers with close-up, wide-shot and medium-shot views of rooftop squatter huts.

'The structures inspire me and let my imagination roam free, and I want to express these through drawings,' said So.

'Everything looks particularly beautiful under the blue sky.'

So and Chung, who have a strong passion for the city's cultural heritage, have also each published a book this month in an attempt to capture Hong Kong's fast-disappearing historical and cultural treasures.

So's book, Very Fantastic, is a chronicle of the making of her award-winning animation of

the same name, which won the top prize at the Independent Short Film and Video Awards

in 2002.

The animation is about a little girl living in a tong lau who dreams up an imaginary world. The book includes a DVD of the animation as well as sketches, character design and illustrations.

'Most people think the animation is the end product, but from the creative process they

will understand how I appreciate and explore the old side of Hong Kong as well as my idea of an ideal space, which is a pre-war tong lau,' said So, who took photographs and made sketches of life in old buildings for her work.

Chung's book, The Art of Treason, is a collection of photographs accompanied by short essays. It is about Tsang Tsou-choi, the self-proclaimed King of Kowloon, who paints calligraphy on the streets.

Tsang's art has gained iconic status in design and fine arts circles around the world.

'This man has been working quietly for 51 years, and all graffiti artists around the world know him. But he is not respected by the government or local artists,' said Chung, who has tracked Tsang's work for 16 years.

'The government has never taken folk history seriously . . . if Hong Kong doesn't preserve its [historical and cultural] roots, it will be nothing but an empty egg shell, which breaks at the slightest tap.'