Usually they get pointed to my old keybindings, which I think are nice, but of course I may be biased from years of using them.
All bindings are rotated through whichever buildings the unit can build
ARM:
Z or shift+Z:
Mex
Twilight
Moho Mex
X or shift+X
Solar
Wind
Adv Solar
Fusion Reactor
Moho Metal Maker
C or shift+C
LLT
Radar
Defender
Pitbull
Flakker
V or shift+V
Nano Turret
Kbot Lab
Vehicle Plant
CORE Bindings:
Z or shift+Z:
Mex
Exploiter
Moho Mex
Moho Exploiter
X or shift+X
Solar
Wind
Adv Solar
Fusion Reactor
Moho Metal Maker
C or shift+C
LLT
Radar
Pulverizer
Viper
Flakker
V or shift+V
Nano Turret
Kbot Lab
Vehicle Plant
For example, if you selected your commander, and you wanted a Kbot Lab, press V or shift+V, and you can place the structure. If you want a Vehicle Plant, press V or shift+V twice. It wont cycle through Nano Turret, because the commander cant build that.
A t2 con will build a viper if you press C once (and not an LLT because it cant build that)
If you keep pressing the key, it will cycle through all possible builds by the selected con(s).
Keys that had to be moved are the following:
FPS mode is now Q
Increase buildspacing is now B
Decrease build spacing is now N