I know that big T want them to cost resources n shit and its ok. Its even ok that stone types do less damage. The problem with stone types is that they take A LOT of time to make making them very very expensive in work time. My suggestion is that maybe all traps should take the same time to build, the steel or wooden trap time (about 50).
Hell, if it was for balance, it should be the steel ones the ones that should take more time, since they are the most effective of them all in terms of resources/damage/work time.
Its not a game changing thing, its a very small one, but its mine.
The problem is here, the stones itself got these hugh work amount. All things you made out of stones need alot more work compared to steel/wood.
If you don't want change that too, you will need special traps for stone exclusive.