So, let's say I have the improvement "Carpenter's Palror", which allows wooden rooms to cost 2 wood and 2 reed.
Then see Brushwood Collector: Each time you renovate or build a room, you can replace the required 1 or 2 reed with a total of 1 wood.
If you interpret this combination in the order Parlor then Brushwood:
It costs 2 wood and 2 reed, then the 2 reed is replaced with 1 wood. So it now costs 3 wood.
In the other order:
It now costs 6 wood in total (brushwood), then the entire cost is set to 2 wood and 2 weed (2 wood and 2 reed).
Which is the appropriate interpretation?