SP- how do I enable Build Options - help!

Hi folks,

Great mod. Love it to bits. I'm playing around with a very simple singleplayer mission or two, to teach myself how to write SCAR code. But I have a problem, and I'm at the 'beat head into wall' stage.

I can't get the 'Build' option to do anything in an SP mission. Nothing, nada. The build menu doesn't even appear when I click on the Build icon.

How do I enable the ability to build units in SP missions?

I've successfully added a build-capable unit or three, and I know all about the various GrantAll/UnrestrictBuild functions. In my M01.lua I've tried:

Player_GrantAllResearch(0)
Player_UnrestrictResearchOption( 0, 'FIGHTER_DESIGNSI' )
Player_UnrestrictBuildOption(0, "Fighters")
Player_UnrestrictBuildOption(0, "imp_tie_fighter")
SobGroup_UnRestrictBuildOption("Production", "Fighters")
SobGroup_UnRestrictBuildOption("Production", "imp_tie_fighter")

( Where 'Production' is a SobGroup consisting of a single imp_fightershipyard. )

I know I must be missing something incredibly basic here. What is it?!