In case you can't find an unoccupied room (at the Department of History and Cultural Studies) suitable for your needs, you may reserve any further rooms of the Freie Universität using Evento. This can be done (approximately) as soon as the lecture period has ended. 

Please use the teaching rooms of the Rost- und Silberlaube, if possible. 
A current overview of the rooms and the persons in chrage of their distribution can be found here.

In case you can't find any rooms in the Rost- und Silberlaube, you may also try reserving other rooms.

Notes:

Please contact the building's gatekeepers concerning the (un-)locking of the various rooms. 

Please make sure to reserve rooms as early as possible using Evento, as this will ensure that the Office of Academic Affairs will be able to process your request and inform the building's gatekeepers in advance.