Old WC3 veteran trying to figure out the SC2 editor

I’m looking into getting into map making for SC2, and one of the map ideas I had was using the zerg base buildings and drone unit to essentially morph infested versions of terran buildings, but have a kind of hybrid race between the two where the player:
Must build on creep
Can only morph certain units from each race
etc

But when I go to edit the drone morph ability, I don’t see where I’d add or remove buildings like you did with the WC3 editor.

Can anyone show me where I’ve overlooked this, or where it might be?

Yup. Apparently you don’t do what you did with WC3. Found my solution.
Edit the unit itself!

Can I get a lock here?

I don’t know about wc3 editor.
It is not as simple as just set which buildings this unit can make.
First thing you need is a button for your building.
Then, in build ability, there is “Ability: Info”, where you set which buildings can be made by this ability (“Button - Building” pairs, doubleclick on it to edit details). Build time is set here, but unit cost is set in the units data for the building you are making. Also, since you talk about drone build, the drone cost (50 minerals) is subtracted from building cost (hatchery cost is 350 minerals in units data). “Technology resource cost” is a different thing.
You can find more details here:
https://sc2mapster.gamepedia.com/Data/Abilities/Build
Then in unit data, you edit “Ability: Command card”. You add a button on command card, set “Command Type” to “Ability command”, select build ability and select a command (it shows only button names from “Button - Building” pairs).
This is just the simplest things. It’s really difficult for me to explain everything about build ability (it took me a lot of time of trial and error).