surely not with a wfp ? the outside should be quickest, rinsing it down first to soak while you start on the inside, i wouldnt have thought 1week, but if you think so, i just think hundreds and hundreds is not going to be accepted by the owner, it will get dirty soon enough and a regular clean might be accepted if you can give a decent price. if its really horribly dirty now for the first clean, i would give them an estimate and then give them the final bill after finishing the week. as it may take longer than expected. work out what you want to earn per hour of work you are doing it , but dont over blow it.
for a big job like this i would probably charge £250 straight off and explain that it will take a long time as it is so dirty over the years. and leave it at that whatever time it takes you, but try and get it done properly as quick as i can??? others may have different opinions...