You can keep old build stats until you confirm

I remember reading a post where someone was confused why the original stats are shown when you don't get to lock them after hitting building.

Whenever you build, you need to confirm in order to apply the stats. The original stats are the ones that are currently active, so you can check if the new ones are actually better or not.

You can keep building again if you don't like the new stats, and just leave it unconfirmed. So if you run out of stones, or you finish your build growth round and decide to save for next time, you don't need to commit to whatever stats you end up with.

Once you roll something that's better, then you press confirm to replace the original stats.

It's not as reliable as locking the stats you want, but given that you need to use everstone everytime(?) you build again with a locked slot with no guarantee that any of the other stats will be any good for awhile, this is a less expensive option.