Hello,
The Workshop has a team bonus aspect if the team all contributes for upgrading. Here are 2 more suggestions I have:
1. Team Donut Generate, Have it take 1 or 2 spots. Have it contribute 1 donut to the team at level 1 every seven days with highest level being level 10. Have it contribute regardless of being upgraded. Have the upgrade cost high amount of resources and time as it is creating donuts out of thin air. Level 10 would create 10 team donuts in a weak with 30 people that would be 300 team donuts which would allow for all 3 boosters and some left over for melons and stun doubles. (This would allow even players that cannot afford to spend real money to contribute to the team donut effort and even out the work load on obtaining the boosters)
2. Trophy Reduction Room. A room that goes from level 1 to level 25 with reducing the penalty of trophies during team fights for 1% to 25% respectively.