Upgrade: Some rooms and teams are variants of or improvements on others. You can change the room or team into the listed upgrade by spending the difference in both capital and time between the original and the new one. For example, if your building includes a Book Repository and you want to upgrade it to a Magical Repository, you can either spend 1 point of Goods, 1 point of Influence, 1 point of Labor, and 2 points of Magic, or spend 270 gp (the difference between the Create entry for a Book Repository and a Magical Repository). You must also spend 4 days (the Time difference between a Book Repository and a Magical Repository).
Pay the price only for types of capital that increase. For example, if you are converting Bunks into Lodging, you spend 3 points of Goods, 3 points of Labor, and 6 days; even though a Lodging costs less Influence, you don't regain any Influence for performing this upgrade.
I think the title says it all, but for the sake of giving a specific example:
I spend 16 days and construct a Common Room, which provides a +7 on influence or gp rolls. I then immediately decide to upgrade it to a Ballroom by paying the difference in capital. A Ballroom takes 40 days to build, minus the 16 days for the Common Room leaves 24 days of upgrade time. During these 24 days do I still receive the benefits of having a Common Room? I don't see any rule concerning it and common sense does seem to pull too hard in either direction (plenty of real world business decide to stay open or close during renovations or improvements).
Thanks.
Whilst the rules are silent (and yes, you could easily argue the case either way), I'm going to throw my weight behind "yes, you still get the benefit of a room that is in the process of upgrading".
My reasoning is fairly simple: the rules are an abstraction and don't cover every single jot and tittle of the effects, but you do still have a common room (to use your example) until the upgrade is complete. And the rules say that if you have a room, it can provide it's benefit. Rather than complicating the bookkeeping involved, it's easier to only have to track the time and not have to remember which rooms are and are not providing benefits.
Yes, this provides an advantage to characters who build basic rooms and then start to upgrade them, rather than going straight for the upgraded versions: they have opened a business and are improving it, but still using it as a business in the meantime. It should still earn them cash/capital because they are using it for that purpose.