I have seen at least 3 or 4 such HTs in India. The cost is astronomical and one has to decide whether it is worth it. My nephew in the US has built a 30 seater HT (with Classe amp to boot) very much like a cinema hall with all the bells and whistles. The cost? - 500,000 US. It is I who uses it whenever I go there. Rest of the time, the room stays locked. I think that is a sheer waste.
In India also such theatres will end up costing between 1 to 2 crores. With such money, one can live comfortably for the rest of his life. Ultimately what is your priority is the deciding factor.
I am involved in 2 projects that involve HT rooms costing some 50 lakhs each. The equipment is just 20 lakhs. The rest go to room interiors. The ambience may be slightly different (more like an living room), but the screen effect and sound effect will be as good.
Cheers