Welcome to BYC.
Other than converting a shed or dog kennel you won't easily find a coop to buy that *actually* holds 10-12 chickens. Prefab coops are notorious for wildly exaggerating the numbers of chickens they can hold, for being shoddily constructed, and for being badly designed.
But since you're in a warm climate you are in luck -- an Open Air coop is both the most appropriate thing for your climate and the easiest to build. Just a big wire box with a 3-sided shelter at one end.
To help you figure out what's best for your needs, here are The Usual Guidelines.
For each adult, standard-sized hen you need:
4 square feet in the coop,
10 square feet in the run,
1 linear foot of roost,
1/4 of a nest box,
And 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
For 12 chickens that means:
48 square feet in the coop. 6'x8' is more practical than 4'x12' since a long, skinny coop like that would be difficult to work inside.
12 feet of roost
120 square feet in the run. 10'x12' or 8'x15' -- 8'x16' means fewer odd cuts than either of those. 6'x20' is possible, especially if your run is an open-topped, fenced area instead of fully-enclosed with a solid and/or wire roof.
12 square feet of ventilation.
3 nest boxes.
The are *guidelines*, not hard-and-fast rules. Here's a great explanation:
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/
This coop in Texas is the primary inspiration for my
current coop build here in North Carolina.