They're built on-demand is there's very little inventory sitting around. Typically the service center here in Portland only has 10-15 on site for delivery.
At the pace they make changes to the car it really doesn't make sense for them to manufacture large batches and those not interested in waiting can pick up an inventory/CPO.
Not sure it's possible to maintain at production targets. 2014 if I recall, Tesla did ~35k units. That's ~12 cars/ hr if we assume 12 hour work days.
Their 2016 target is 100,000 cars or 33 cars per hour by 2016. So for example they'd have to both double their plant capacity then get 50% better at making cars. Seems like a tall order but perhaps doable for a guy like Musk :)
From what I've been told, the plant they make them at is only fractionally used. I would assume that means there is plenty of room for production line growth if they need to do that.
At the pace they make changes to the car it really doesn't make sense for them to manufacture large batches and those not interested in waiting can pick up an inventory/CPO.