What is the ruling on decorating walls and ceilings with what is known as "gypsum board"?

Decorating houses with gypsum is not forbidden, unless it is accompanied by a Sharia-prohibited act such as extravagance, wastefulness, or depicting animate beings. As for ornamentation with materials other than gold and silver, there is no harm in it as long as it does not reach the point of extravagance.