Instead of having to save up 100+ tools to upgrade the barn, give to option up upgrade 1 or 2 spaces at a time.
Eg: you have 50 bricks but only 12 wood.
To upgrade one space would cost 12 of each item. You can choose to upgrade the one space available instead of waiting to collect the rest.
I sell tools all the time to give myself more space only to find id have used them not long after.