How would I go about combining many blocks (to negate from the baseplate) and the baseplate in a union to create a specific shaped hole?

[BigExplodingDonkey]

I’m trying to use these parts as the negated part. ^

And I’m trying to use them to negate an arena sized hole in the baseplate… any ideas on how to do so?

[minecraftwolf1978 (Lolz)]

Select all the parts, UNION them, THEN negate them (& if the weren’t already touching the ground to negate, do so) Hope this helped!