The box you build around the plant: how a room is laid out, how air moves through it, what the heating and cooling equipment has to be sized for, and the design decisions that are cheap on paper and expensive once the walls are up.
Tent grows, sealed rooms and converted buildings each have a different set of constraints, but the same order of work. Envelope and insulation first, then the climate equipment sized against the actual heat and moisture load rather than against floor area, then lighting layout, then irrigation, then the electrical supply that has to carry all of it safely.
Two design mistakes account for most of the retrofits. Dehumidification is undersized because the calculation used the room volume instead of the water the plants will transpire, which in a tropical building is a large number. And there is no plan for air movement inside the canopy as distinct from air exchange with outside, which is the difference between an even room and a room with a mould pocket in the middle of it.
Where to start