Why a Gazebo's Roof Size Isn't the Usable Floor Space
A gazebo's roof overhangs its structural posts on every model in this range - the number in the title describes the roof, not the space between the posts, which is always smaller and is published separately on the sizing pages.
What the title's size actually measures
A listing titled “10' x 12' Outdoor Wood Gazebo” is describing the roof - the largest single measurement GARTOO publishes for that structure, and the one that ends up in the title because it is the biggest number. It is not a claim about how much floor space is available to stand or sit in underneath it.
Why the roof is bigger than the frame
Every free-standing gazebo in this range - wood or steel, double-top or gable roof - has a roof that extends past the structural posts holding it up. That overhang is what keeps rain and runoff clear of the frame instead of dripping straight down its legs; without it, water would run off the roof edge directly onto the posts and the ground at their base. The trade-off is that the covered footprint between the posts, where a table or seating actually goes, is smaller than the roof size in the title.
What "usable footprint" means here
Post-to-post distance - the clear space between the structural legs - is what this site calls usable footprint, and it is a separate figure from roof size on every sizing page, collected by hand rather than assumed from the title. Where it has not yet been measured, the page says so rather than estimating it from the roof number.
The one gazebo this doesn't apply to the same way
The range's wall-mounted lean-to gazebo does not have a post-to-post footprint at all - one edge sits against a wall rather than being bounded by posts on every side. See wall-mounted vs. free-standing for how its sizing question is different, not just smaller.
Questions
Does the roof size ever equal the usable floor space?
Not for any free-standing gazebo in this range - the roof always overhangs the posts by some amount. How much is what the sizing pages publish as it is collected.
Is the usable footprint published for every gazebo yet?
Not yet for any of them - it is collected by hand, not estimated from the roof size, and each sizing page shows a pending measurement as a dash, not a guess.
Does the same overhang logic apply to the party tent, shed and carport?
The general principle - stated size versus usable space - is checked the same way on their own sizing pages, though those structures aren't built around a post-and-roof gazebo frame in the same sense.