There's 2 benefits of joining a guild... 1, Getting a guild quest daily and receiving guild coins for completing the quest and 2, guildies helping out with resources.
But I feel like there's something missing. Guild leveling will be nice, where a % of each members experience goes to the guild, that's where a few buildings come in. Purchasable buildings from collected coins of each member's island, meaning, a member can buy a building that produces coins for the guild or can be donated. The more members that buys this building (upgradable), the more coins can be sent to a bank for the guild. So those coins can be used to upgrade the guild bank, and so more buildings can be bought for the Guild as one to give players more experience, faster coins ect.
Buildings I have in mind:
*Coin Donation - Where a player of a guild can purchase this building to donate coins to their guild.
*Guild Bank - Where all member's donated coins go to.
*Exchange Office - Where a leader can exchange coins to guild coins from the Bank.
A building that can be upgraded to:
*Gives members % of extra experience collected from adventures
*Gives members % of extra coins collected either from adventure or treasure search
*Gives members an additional daily quest
*Gives members a random adventure daily (the higher the level of this building, the better the adventure)
In addition, a lottery building will also be nice. For example, whenever you play lottery, you can either win resources, an adventure, experience, coins, gems or 1 day premium. This should cost coins, depending on your level, this will be the reward. Like level 1-20 players gets basic items.
Hope it all makes sense, if not, please mail me to clarify