Silver Creek Portable Buildings offers sheds, add-on rooms, and yes, complete tiny houses (with and without trailers), and they make it pretty easy to get one. They ship nationwide from small-town Snowflake, Arizona, and they accept credit cards and offer a variety of payment plans as well as a rent-to-own option. Prices aren’t too bad either, going from $30,000 to $45,500 for their 12× trailerless range (the $39,500 12×24 is what you see in the pictures).
h/t Tiny House Talk
Customization is possible, but standard features include tongue and groove siding, a sheet metal roof, two entry doors, double pane windows and spray foam / fiberglass insulation, an on-demand water heater, and painted drywall and carpet or linoleum inside. Alternatively, you can get a “kickstarter” unit with the framing, electrical and plumbing work taken care of and finish it up yourself.