I'm expressing my views here:
I don't know why but i don't see all hate for Dashanan over here and what he told to Nandi was justifiable by any means. If you are building Bhavan for Shiva and after it being completed you would want to tell the same to Shiva yourself and not by sending someone to tell it. Its more like insulting Shiva if he (Dashanan) himself doesn't go to tell the matter to Shiva.
CV's use Nandi to make small matters Huge in the serial and they do a good job of it. First it was with Ganesh, which prompted Shiva to cut his head and now it seems to be Dashanan's Bhavan. Nandi has no reasons to be angry just about now as the Bhavan is for Shiva.
I don't get it, Nandi is Shiva's Vaahan and that must be greater than being his Paaram Bhakt is what i perceive, there is no need for it to be said? does it?
Finally i hope they justify Dashanan turning to Raavan as so far i seem to find nothing bad about his behavior which seems to be quite normal for anyone.