Invitation letter for my parents to come visit me in China

I am currently residing in Anshan China, my contract expires on the 24th of January at such time I will return to South Africa.

I would like to have my parents visit me a 2 weeks prior, to show them around, and fly back to South Africa with them.

A friend of mine, Chinese citizen, said she will write the letter if I can give her the format.
There isn't a lot of example invitation letters, maybe I am looking on the wrong websites, any help and suggestions are welcome.