Conduit in trench is important within the greenhouse no pvc or flex plastic. Make sure to not undersize the circuits (add up anticipated loads) and install a disconnect at the greenhouse before the branch circuits..
Make sure all the runs are thwn in conduit and carry a ground. Needs to be designed for "wet locations" and gcfi's..
Insure electrician properly grounds and does not energize the frame of the greenhouse. Additionally any cable used to lighting or equipment should be rated sjoow.
I thought the OP said the greenhouse was "pre-wired" and only needed the service entrance?
Prewired only indicates it's there. No indication of code or suitability. The "cable" pertains to that used from gcfi to fixture or appliance.
Greenhouses degrade due to exposure, UV and moisture. Locally there are lots of greenhouses, some done right, some are shocking experiences.
