I would recommend an enclosed area in which to lock the bikes onto racks. Maybe the powers that be on this project are all for incorporating this area into the building itself, and having bike-sized lockers (with ventilation, but you can't tell from outside the locker whether it has a bike inside or not). That would probably be ideal. Since a thief can't tell if the locker is empty until he breaks into it, the locker system is known to be an effective theft deterrent. As a secondary measure, inside a locker, there should still be a way to lock the bike to the wall or locker side.
If open air / outside the building, it would have an iron fence that meets the roof (can't climb over) , and a keycard entry gate. Each person who wishes to use the entrance would have to sign up for an individualized access card, even if it's free. System would log when people enter and exit. Security camera running. The exit/gate unlock button would be on the opposite wall from the door and inaccessible from outside the fence. Upside-down U bike racks to lock, with adequate space between each one, and between racks and walls.
Also generally, avoid situating the storage area in a little-trafficked, secluded spot. Seclusion means that a thief can make an attempt with more confidence that there will be no eyewitnesses. Do not hide the area with shrubs or put it out back somewhere.