A good idea, but instead of another building it could be an add-on the Clan Castle, maybe just another button next to request troops that could lead you to a screen to deposit them.
Yes
No
I'm in the middle
Pretty good idea. The only problem I can really see is spamming donations, but really, is that a problem? :P
Scarred Gold Elder
I love this idea it's great! Now I love donating to my clan and I always want to make some wizards or dragons for them but I also need to raid so I use my barch army and I'm not able to donate as much. I hope that supercell sees this idea and chooses to implement this as it is great.