Maidens can produce offspring in ANY building as long as they have food,
water, and a mate. ;)  They do it faster in peasant huts, but by keeping
some in other buildings you assure that those buildings get replacement
workers even if there are no 'spares' in the castle and also you increase
the moral of the workers in that building so they stay healthier and don't
want to kill themselves.  Happy workers are good workers as long as they
are also healthy and well fed.  That's all maidens do but these functions
are totally critical to your society.  Keep maidens in every building if
you can, but especially in your most important buildings.  Put maidens
where the men are in other words.  Your men will thank you by living and
working better and your tribe will increase faster.  Just make sure
everybody has food and water, and preferably all the foods they like.