Accommodating an au pair outside the family's home is not really conventional within the context of the au pair programmes. The au pair and host family should really both live together as one family.
We cannot provide a specific suggestion, however, we can give you our personal opinion. This situation is not very ideal, however, it is acceptable when it is the only possibility due to space limitations. But even in such cases, the following applies: an au pair should have his/her own heatable and sufficiently furnished room, at least eight square meters in size. It should have a lockable door and at least one window allowing sunlight into the room. Clean sanitary facilities are also important.
The personal connection to the host family is a very important point. You need to make sure that you and your au pair spend as much time together as possible. The au pair must be integrated into family life and learn more about the culture of the host country. This is all part of the basic concept of au pairing.