I think "Because you would like to have a castle." should be accepted. Of course this would translate to "Protože bys chtěla mít hrad", but I think the having is implied strongly enough, because what else would you want? Be one? Be romantically involved with one?
This is a very not intuitive sentence... A better one could be, for example, "Because then you would want an ice-cream too!" or "If I gave you a finger you would want the whole hand".
I think it is being introduced right here. It uses the past participle + a special form of "bych/bys/by...".