I am not a professional pilot by any stretch, but a long time lurker - over the years I've learned a lot of interesting stuff!
But I am a Glaswegian. The junction that the Clutha sits on is larger by some measure than the Clutha's roof, is relatively quiet at that time of night due to the bus lane and being relatively far away from the real nightlife.
A view of it is
here. Would a pilot really choose to land on this roof if they had a choice in the matter? Moreover, the buildings in that block aren't exactly known for their structural integrity, which any local can vouch for.
But regardless I'm sure the AAIB will get to the bottom of it. This is a really sad event for the crew and the casualties on the ground - no one should have to go to work (or for a night out, for the matter) and not come back.