They're a tender perennial. How big it will get depends on whether you can give protection in winter. I had one that I bought last spring. It was just starting to flower when the cold weather arrived. I don't have a greenhouse and it was too large for a windowsill, so I tucked it into a friend's polytunnel. As we had a very cold winter and the polytunnel was unheated the top growth froze and died, but it has started growing again from the roots. Now about 8 inches high. I'm sure that if you have a conservatory or suitable greenhouse you could end up with three spectacular bushes.

As above.
I did find that the tap water around here caused "lime scale" to build up on the leaves, so try to water with rain water, or allow the tap water to breathe in a bucket for at least 24hrs before using.
Mine bloomed well into December in the conservatory.

Thankyou for advice.As I don't have means of protection for the winter , I think I might grow them on for a while and then pass them on to friends that have greenhouses.

They'll love you!

How's this for a plan (if you have a garage) - give two away and keep the third in the garage. Give it a good watering before putting in before the first frost, and then the merest trickle of water every now and then. Bring it out on the warmer days of spring having cut it back to 15/20cm and give it a feed. Put it under cover if there is a risk of night time frost. Mine was outdoors from mid March onwards, although it is only really starting to look happy now.
Check out my photos at the link below if you need convincing that it's worth the effort........

http://www.growsonyou.com/garden/show_garden_item/29400-tibouchina