Westin - Rollaway Bed Charge?
Westin's rooms with adjoining doors only paired with two double beds in one room and one king in another. What was their rollaway charge negotiated with the group rate?
As an alternative, most hotel rooms are large enough to accomodate an air mattress, which i've packed into my luggage before without mishap. Just remember to pack bedding for it as well.
As a follow-up suggestion, I recommend inspecting and testing one's air mattress a decent amount of time before the convention.
At a prior con, I discovered upon arrival that I was unable to get a double room, but had very sagely packed my air mattress so I'd have something to sleep on in case this happened. However, I had not-so-sagely failed to inspect the mattress prior to packing, and discovered after inflating it that it had a leak and was unusable.
After realizing just how uncomfortable the bare floor was, I then discovered that lying in the room's easy chair with feet propped on the desk chair was actually a quite serviceable sleeping arrangement, if a bit less than ideal. 
yea they don't have a warehouse full of rollaway beds, fridges and stuff so grab em while supplies last.
Rollaway beds are no charge as I recall; but they are in short, short, first-come first-serve, they all vanish Wednesday, supply. You should not count on their availability.