Design mode not showing up in campaign

[Chaza]

I'm new to this, so I'm not sure whether I'm just being silly and that design mode should show up at the end of the level. I'm on the first level, and I have discovered various turrets, yet I can't access design mode in order to use them. Can anyone help me?

[KukY]

You have to build HQ (Command Center) to have design menu, minimap and to be able to build any defensive structures.

[Chaza]

I've built a command center, and I have a minimap and other structures, but no design menu.

EDIT:
After checking again, I don't have a minimap. I'm still able to build other structures though.

[Zarel]

Command Center is only required for defensive structures in MP...

Anyway, try demolishing and rebuilding your Command Center.

[Chaza]

Rebuilt my command center, everything is fine now. Thanks.