After a certain point, i might also have to keep 1 builder free for walls.
1- Currently, because of low build times, i can always get 1 builder free after every 1 day. I also do long upgrades along to delay it as much as i can. it's complicated to explain. once all upgrades have minimum of 7 days worth build time, i will not be able to get free builder too often. ( but reaching that point will take lots of time because i delay it by mixing long and short build times:D )
2- Once my legos finish up, i won't be able to empty my storages totally. Currently i saved some legos for that purpose( to spend 8 mil totally) but i will run out of them sooner or later.

