Swift Shelter 3m x 3m Gazebo with sides!
Should be able to get one for about £250 and these are commercial quality so will go on and on (unlike the £50 rubbish you get in DIY stores – won't keep the weather off, won't cope with high winds, won't last).
Had mine 7 years now, used it in three locations last weekend alone. Had no problems with it whatsoever since i bought it, everyone who sees it wants one!
Used it camping many times and my one is fully waterproof.
Make sure you get a steel frame as the ally one's are prone to breaking. Get a £20 fold flat trolley if you need to carry it any distance as they are heavy.
Remember, you get what you pay for!