This is very back of the napkin guesswork, but here goes: If part of the pitch is that, more than just "vertical" farming, it is "vertical urban" farming (e.g.

This is very back of the napkin guesswork, but here goes: If part of the pitch is that, more than just "vertical" farming, it is "vertical urban" farming (e.g. for logistical advantage of proximity to demand), that would imply potential proximity to other tall structures in a city. Probably taller structures. You would have concerns for consistency of sunlight. Also only the edges of the building would get it, so you would want your farm to only occupy the tiniest edge footprint of the building, but across multiple floors. That is an odd sort of lease to get from a building. Even a new building built nearby after a year or two could destroy the efficiency of your once-carefully-selected site. Another under-educated guess that I would be happy to hear about from someone more knowledge: I would guess that glass facades costs more than other materials.