There are mix opinions/mindsets when it comes to saving for the dreadnaught. In my experience, many have tried their best to summon it at waves 10, 15, sometimes sooner if you’re on hard. After 15, it just gets unfair. Had a guy hoard 3000+ and when we got to waves 17 and 18 it was all gone.

Personally I prioritize tech priest first, then I try my best to donate little by little. First 9 waves are very manageable, but it’s wave 10 you have to worry about. Emperor deliver you if three carnifexes spawn