I improved the rules from his thread(The map isn't really 25x25x25 in his challenge) and created this thread.
1. If you create a 25³ map just post like a normal map and send me a link to the thread (you don't need to create a thread if you don't want to though, you could just post it only here as well)
2. The map has to be 25x25x25 or less. It is NOT allowed to place redstone or command blocks outside this space.
3. The Lobby/start area has to be inside the 25x25x25 area
4. The map must be playable without mods
5. The map has to be built in a 27x27x27 bedrock box, the bedrock can be replaced with air, barriers or glass, but not with any other block. (If you want to use a different block ask). You can use structure blocks and commands like /fill and /clone though.
6. (optional) Call your map "25³ Name" or "25^3 Name" or something similar to make it clear that it's a 25³ map. (e.g. 25³ Buttons)