A concrete slab can be formed and cast in a day for a relatively low cost, particularly if you provide the labor. But casting concrete can be a challenge for inexperienced do-it-yourselfers.
A built-up floor is more attractive than a slab but can require exacting carpentry skills. A built-up floor also sits a little higher above the ground than a slab.
A gazebo’s posts are fastened to the foundation or a sill of treated 2-by lumber with post anchors. The tops of the posts are secured to the beams by metal hangers or post caps; alternatively, you can toenail through the beams into the posts. Knee braces ensure a more rigid structure.
The rafters radiate outward from a central hub and are joined to the top ends of the posts or to the beams. The gazebo may be capped with either solid or open roofing.