Water Pumps (to clear flooded patio).

vaio

I suspect you'd be lucky to get it to start pumping in 2" of water, you can get dedicated “puddle suckers” which will start at 45mm and pump down to a couple of mm but these are £££

Best solution by far is a sump as others have said. You can reduce the foot print of it if you use a pump with a magnetic float in a tube rather than on the end of a bit of cable

Wookey

Another option would be to use a water butt pump, would still be best to create a sump for it and then just drop it in and turn it on as and when you need to. Most have a fine filter contained within them and there pump rate would be slower than dedicated sump pumps which would tend not to suck the sump out in a few seconds.

GreenSheep

This may be overkill for a patio.
Flow rate on these things is massive for domestic use. Even the little ones.
I drained a big hottub using a small one once in a few minutes.
If this is just a couple of times a year and not really a big deal I would buy a drill pump from Maplin for £10 and mount it to a bit of MDF.
The flow on that thing will supprise you and very little to go wrong.
Less to move around and store and will be quicker overall to setup and use than a submersable for a patio.
Although if you do want to go for a submersable defo build a little sump.
A little sump would be a nice little project for a Saturday afternoon and cost very little if you recycle something for the lining, etc.

Cheers, GreenSheep