I wasn't sure whether you were asking about the grammar, or whether you wanted an actual answer! If you wanted some sample answers, then Dan has given you some nice ones above. His reply also points up some differences between British and American English. Our tense use is the same, but the adverbial phrase about the weekend is different.
What are you doing at the weekend? (GB)
What are you doing this weekend (US/GB)
What do you do at the weekends?
What do you do on weekends? (US/GB)
And, if you are interested, this is one of the few cases where Australians and New Zealanders follow the American rather than the British usage.
If anyone would like to correct me on this, or add to it, please comment!