OK: I have a lot of things to say about this one.
1. The placement issues with blocks.
Very often during building, I get stuck in blocks and it slows me down a lot. Blocks will also frequently disappear and need to be replaced within a second of placing them when you build quickly. Deleting blocks is also a pain as they will sometimes reappear and trap you in them, making you stuck and have to spam buttons until you can get out.
2. Limited block choices.
I cant find any skeleton skulls or any of the mob heads. There are also a few other blocks missing, but I'm sure you already know.
3. Duos?
I know this game is in early release, but I wanna mention this before it's finalized. Make a duos game-mode for this, it'll go a long way.
4. Build height.
Make the build height higher. I know this sounds crazy since you have so little time, but it needs it. The arena itself is very small, which means you need to make up for it with the amount of higher up space you have.
5. Make it more accessible to change your vote.
Once you pick something, you can't unpick it from my experience. I find myself accidentally picking a build and then looking closer to realize it's an inappropriate build or something.
6. Add an NPC in the corner for you to change the floor block.
As a Just Build main, having the /floor command is great and all, but it's simply not accessible to new users. They get confused and most of the time over half of the lobby didnt even set the floor. Take a more Hypixel approach on this one. Having the ability to change the floor in this would be incredible!
A couple of things I want to add, I LOVE the option that you get to "choose" between 2 builds instead of having multiple blocks to vote with like in Hive Just Build or Hypixel Build battle. It makes voting a lot more fair, and I think this was a great thing to add!
This game-mode is very unique. While Build Battle is fun, it's everywhere. Glad to see some innovation with new modes!