We built a platform in our garden for a gazebo kit to go on and used a Spantec deck frame with treated pine decking.
Spantec were great, designed the deck to be the perfect size to go under the gazebo and gave us advice which was really helpful.
We needed a hexagonal deck to go under the gazebo kit, building it was really simple with the kit we got from Spantec. Everything was cut to size, it was just like a big kids meccano set to put together. The hardest bit was the piers but they gave us advice that helped us with that too.