The great thing about sand is it can be made anywhere really as long a the floor takes the weight. Having tonnes of sand and a floor like this could be a problem if there is a basement below. Luckily this wasn't the case. I do do lots of sculptures indoors and it has it's good thing and bad points.
For me working outdoor in the elements brings another dimension to my work because I still have to deal with the weather but I like the open air. Working inside can be nice but I start to feel claustrophobic.
A stable light means I don't have to keep worrying how the sculpture looks at different times of the day , with different shadows. My work usually involves the play of light and shadows, if that makes sense. So, the location and environment dictates a lot about a sculpture.