You will need to have it rezzed on some land. Here is info about land and group land:
Land and houses 2012
When it is rezzed, edit the building. In the edit window, you will find a place where you can deed the building to the group that owns the land. Before you deed land to the group, read the cautions in the article above.
Deeding objects to a group can create problems, so I recommend that you look into other options first.
You can give other people the power to edit your things. They could then edit your building (and anything else you have rezzed).
I am assuming that the building came with mod perms. If not, no one will be able to edit it. But people can put things in it if it is on land where they have build rights. You can give build rights without deeding the land to the group. You just set the land to the group See this article:
Groups 201, advanced
TKR
