Since the changes from Dakota, as mentioned in other solutions, it's much easier now to get Tier 10 milestones by using add/subtract terrain (rubber bands on both LT RT triggers) or by placing Lightbulbs (or Sound Effects, Paths...), if you simply only want this achievement.
Anyhow, I still recommend that you use my "Tier 10 Milestone TA" map, if you want to grind the milestone "Total Community Worlds Played" and to obtain other 100 hours achievements (MTV, Comedy Central, VH1...) in parallel.
-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-
There are various milestones for you to level up to Tier 10. However the easiest Tier 10 Milestone is "Total Community Worlds Played". So you have to play 100 hours of community games.
Simply load up a community game that does not automatically end. Just let it run over night. So you will gain 7-9 hours per night.
Make sure that the Xbox controller is plugged into the USB port. Otherwise, when the controller is idle for a while, it will be automatically off and the community game will be paused.
While in the community game, You can check the progress by pressing
then
to load your profile. "Milestones" can be found under the "Challenges" tab. Navigate to the right a little bit, you will find the milestone "Total Community Worlds Played".
PS: I suggest that you also snap a video app, for example Hulu Plus, to obtain other 100 hours achievements in parallel.
PPS: I made a minimal map for you guys. Search "Tier 10 Milestone TA" to play and grind this achievement. It should consume the least Xbox/PC resources.
It seams the timer reduced to 64 hours for tier 10.
Toamikel mentioned.
"Also you can run the X1 and Win8 versions concurrently and they both add to the timer. So you can cut the total time in half by doing that."