I've successfully grown rhubarb in a pot on the patio. It was a very big pot
though - one of those 'tough tubs' as sold by Wickes the builders merchants
with lots of holes drilled in the bottom. I think B&Q and other DIY stores
sell similar large tubs. They 'may' be cheaper than buying a big container
pot from a garden centre so worth investigating.

Best to use a mix of garden soil (and well rotted manure if you have access
to any) rather than potting compost as this dries out too quickly.

It will need plenty of water and feed - I used Miracle Grow and had a good
healthy plant.
The keys to success are - big pot - plenty of water in hot weather - plenty
of feed.

Norman Digger.