I am in construction, most of the construction is Reinforced concrete, and windows are all aluminum, so that leaves only formwork and fitting out.
Legally you will need a working visa, and attend the mandatory safety training course to get on to site. Cantonese is the site lingo.
Freelance work is rare, most fitting out work is constructed in China requiring installation only here.
I only know of one expat carpenter, he makes outdoor furniture (tables, chairs, etc) and in high rise buildings here there is not that much demand.
sorry I couldn't bee more positive - hope this helps.
cheers,