In general, the trailer industry (enclosed) considers anything beyond a basic trailer to be an options trailer. Basic means that it has a standard plywood or OSB floor, no floor covering, insulation, no special lights or wiring, etc.
There are many options available depending on the brand. They can be simple such as rubber tread plate (RTP) floor covering, to bathrooms, A/C/ generators, live in quarters, cabinets, and many others.
Option trailers take longer to build than standard (cookie cutter) trailers. When a basic trailer has been completed, it then must go to the options department. Most of the time the options department is backlogged which ads even more to the time for options to be completed. Actual work time needed to complete the options depends on the complexity of the options.
Even though it may take longer to get an options trailer completed, it is well worth the time to have these features installed right at the factory.
There are companies available that only provide installation of options.
