Anything that you can destroy counts as a block. The following levels can be used to grind your total. Play level 5-19 and use the three birds you are given to destroy the three large piles of miscellaneous blocks. Hit the bottom pile first, then the top, followed by a shot aimed towards the far right to clean up. You can destroy at least forty blocks per attempt of the level, netting about 150 blocks per minute. You can also try level 4-13 but it is highly variable and trickier to make the necessary shots. The most important part is to hit the trees. They can be completely destroyed with one hit and contain about fifteen blocks each. This level can result in about 80 blocks per attempt.