I think you need the word "ceiling" in there.

http://www.hotelchatter.com/story/2006/9/18/92155/7048/hotel...
Located in the basement the pool has a starlit ceiling

http://granddesignslive.com/saffron/
offers diners exceptional food in a relaxing, stylish venue that features a star-lit ceiling and stunning water feature

http://www.moboces.org/docs/CIS/NewsNotes Nov 04.pdf
The new LMC is centrally located in the heart of the school. It features a star-studded ceiling and a full wall of windows.

http://www.inetgiant.com/AdDetails/Charming-Log-Cabin-Branso...
The bedroom has a star lit ceiling for those who want a romantic getaway

(Despite these "star-lit" and "star lit" examples, I think "starlit" might work best.)


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Note added at 1 hr (2010-11-18 17:18:49 GMT)
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I'm glad it helped. However, you may want to ask your client if this is an open-air or enclosed spa. My answer was based on the idea that it is enclosed.

http://www.etihometheaters.com/home-theater-decor/ceiling.ht...
We have seen starlit ceilings in restaurants, luxury ocean liners, night clubs, spas, planetariums, high end shopping malls, theater houses, casinos, award shows, and even hospice and cancer treatment centers...

It is only natural that we should also wish to admire the starry skies in the ceilings of our homes. It is becoming “in vogue” to add a starlit ceiling in one’s home theater...

Its popularity has been made possible by modern fiber optics, which enables the creation of deeply impressive starry skies. With a single projector, hundreds of stars can be illuminated.

Another way to get the effects of a starlit sky is the application of specific paints and techniques. We have a local artist who does these “sky murals”. These murals can be impressive as and even more detailed than fiber optics. Although if you were to combine them both … wow!!