Now this is my kind of pergola. The canopy is retractable and can be moved dependent on the weather (very apt in the UK). It's also UV resistant and water drains safely (in case you're having a water fight). It comes with 16 stakes, a bit overkill in my opinion, but it helps to make the structure more sturdy and wolf blow resustant. The frame stays strong for years and is powder coated and rust resistant. Obviously if you smash it with hammers it won't stay strong, so don't do that
 
The dimensions of this pergola are 350L x 350W x 230Hcm. Here are the assembly instructions