Now for the walkthrough:
For waves 1-10, I just started building my Maze with basic towers and as you can see, one AOE range tower:
Wave 20:For waves 11-20, I basically continued the maze except I upgraded my AOE tower, built a stick-man tower, and built a static floor tile. A good strategy throughout the game is to build more towers that you can afford instead of saving up for the bigger towers(at least on medium), then wait for the boss levels before you purchase the really big upgrades. Otherwise too many creeps will slip past while your waiting for upgrade money.
Wave 30:At wave 30, I had just about upgraded the stickman tower, the AOE tower and the static floor tile to max and was waiting for money for the boss tower. Waiting for money is generally not a good idea in this game on normal.
Wave 40:At wave forty, I had already built two boss towers and upgraded 1 of them twice. I also bought 1 electricity tower and upgraded it to the 2nd to last upgrade.
Wave 50:At wave 50 I had 6 boss towers with two of them upgraded to full and the rest upgraded to next to full. I used the boss that gave 500,000 or so to upgrade my first boss tower to full and then used some money from the following two waves to upgrade the other one. 50 was the last wave and I beat it. This strategy of laying out an extravagant maze probably won’t work on hard as it was cutting it close at times just on medium. On hard, you’d probably have to group all your towers closer together with the boss towers near the center and above the static floor tile. Use some serious slowing effects of floor tiles to slow the creeps and AOE lightening to help with the earlier levels(pre level 40).