Clash of Clans syncs almost in real time, but it doesn't tell you that you have disconnected from the game the moment you disconnect from the game. Starting at the disconnection time, Clash of Clans will attempt to reconnect. If it doesn't connect in a specific period of time, it will give you the error message. If you exit the game before re-connection, it wont save the changes. You may disconnect from Clash of Clans but still have a stable connection to your Wi-Fi or data. Before exiting the game, I always find a multiplayer match (because that requires a connection to Clash of Clans) then exit the game to ensure that my changes have been saved
Yes this is possible. What your friend is going to need are at least two Google accounts linked to his phone.
First, from within Clash of Clans, go into settings and connect the current village to a Google+ account. This will allow him to restore his village from any device that he signs into his Google account from.
Then in Android,go to settings -> Apps -> Clash of Clans, and 'Clear Data'. This will wipe the village off the device, but it will still be linked to the Google+ account.
Now open Clash of Clans again and get past the intro tutorial. On your iOS device, open Clash of Clans, go to Settings -> Link a Device -> This is the old device. On the Android phone, open Clash of Clans, go to settings -> Link a Device -> This is the new device. Follow the steps to link the Android phone to your village. Now connect the new village to a second Google+ account (Must be different than the first one!)
Now any time he wants to switch between the two, he just simply needs to Clear Data as explained above. After loading Clash of Clans, he will be able to sign into a Google+ account (there's now an option to do so without doing the tutorial), and restore its respective village.
I just tried this entire procedure and verified it works.
For future reference, it appears that Android phones will soon be getting user profiles. So that like Android tablets, different user profiles store different sets of user data. When this feature comes out, it would be possible to setup each village on a different user profile and just simply switch between the profiles, no clearing user data needed. Though I would always recommend linking each village to a Google+ account for safety.
Best Answer
Specific buildings have different weights
For example, x-bows and inferno towers have high weight so building them would increase the weight of your base, making your war mirrors base to be harder and more levelled
This link shows weight comparison an example of how it effects match making as the game attempt to find a war where all player have an even match https://www.clashtrack.com/images/weight_comparison.jpg
The higher you war weight, the higher level your opponent (mirror) in war would/should be
https://www.clashtrack.com/en/war-weight