I liked this event on Beta, and even though they nerfed it a bit, I still like it. Getting the main event building without diamonds is very doable.
If you want the event building without spending some diamonds there are some hints to keep in mind:
1) Use up tickets daily to ensure you always keep the count at 2 or less.
2) Make going for Paws the first priority. No matter how tempting it looks, the chests are not worth it. Don't add blocks to make a chest bigger, except if it is to help free up a Paw. (Unless you really don't want the event building; but it's a great building for most cities).
3) save up coins. Don't buy a single tool or small set, no matter how tempting any one board looks. Keep saving coins until you can afford the large set. Once you have the coins, late in the game, you'll have a good idea of home many Paws you need to get the vent building, and how to space out the use of the tools for the rest of the event.
4) Take your time to think about how to arrange to colored blocks. As time goes on, it gets easier and easier to see promising arrangements (but avoid the temptation to waste a move just to get a chest: focus each move ONLY on what is needed to free a Paw).
Edited for typos and to add 2 more hints.
5) When consolidating blocks, for the most part it is better to start at the top)