Hi lupchiancristi,
In my experience of cleaning many different places from (hospital floors and wards to housing association entrances and stair wells, to offices and small factory units), you really need to base your cleaning on an hourly rate as Drew says.
Looking at your outline of the property, I would guestimate it will take you at least two hours a night to clean the office and bathroom/toilets plus the rest of the items in your posting, using a rota system, cleaning windows once a week and other items another night. I would vac all floors every night and dust desks if on the list every day.
I would recommend before you take the job on you draw up a through cleaning schedule/ rota with the help of the customer, regards what they want cleaning, what time of the day they want their cleaning done, and who will be responsible for providing the equipment and chemicals to clean the premises.
Will you be a key holder for the premises? And go in to clean when the place is empty, which can make cleaning quicker. Or will you be expected to clean in the day when staff are working there, which in my experience will take longer to clean.
I clean in both situations and personally prefer to clean in the evening when no one is present, although you still have to be just as through in your cleaning, as staff will pick-up missed bits of cleaning in the day and leave sometimes sarcastic little notes!
Hope this helps. If you need any more advice, please feel free to email me. Private email address in my profile.
Regards Phil
