don't know if someone made this,so i post it here.
i make buildings be constructed through command center like in previous C&C games:
the non-buiding area that surrounded command center has been extended. or the building you placed would not start constructing. And enlarging this area also is necessary for extending the buildable domain. I had extended the buildable domain without enlarge the non-building area sometime. But I forgot how to do it ...
now let's build:
construction complete:
