Don't try something that has never been done before. It hasn't been done for a reason. Most things that haven't been done, have at least been tried and failed. It's because indoor maps often fail due to it being a 1 hit kill game - with jumping as a priority. Grass-outdoor maps will always be the most played map choice, so play to the favourites.
It's rare for an indoor map to have good gameplay - people try and fail with it - DP doesn't let you get the detail you'd need - and outdoor maps are the easiest. Stick to what works, and what has worked. It doesn't matter if there's already a bunch of outdoor ones, they all look different and this game already has way more maps than just about every game. It's not about being original - its about finding a map that works for the game. Look at league of legends -> 1 map -- not the best example, cause its a different style game, but its the gameplay by each team that causes games to be interesting. Many competitive games only have a list of 3-5 maps that get played. Don't bother going for creativity, if you can make a map thats outdoor/grassy better than a current one, then do it - and hopefully it gets played over a current one. Simple.
Anyone who says different doesn't understand what they're talking about.