Make a backup of your project before following this guide.

Go to the BP_SGKBuildingInterface and copy the video below.

Go to the BP_MasterBuildPart and create a new Variable called IsFoundationStairs and set its type to Boolean. Then compile and make sure the Default value is unticked. Then tick on the Instance Editable option.

Next copy the video below.

Next go to the BP_SupportComponent and copy the video below.

Next go to the following blueprints Class Default and tick on the IsFoundationStairs setting.

BP_MetalFoundationStairs

BP_StoneFoundationStairs

BP_WoodFoundationStairs