At the most, I would suggest 30 to 40 minutes a side. Multiply that by your hourly rate.
There are always a couple of issues you need to consider. When would you do it, foot traffic and vehicle parking? When I'm asked to quote, I ask myself if this is a job I could do when the building is closed. It makes things much easier if you don't have to deal with pedestrians and traffic.
I do believe that the worst part of the clean is going to be those glass canopies. We had them when we cleaned the local school. They consist of flat plates of glass which are the linked together with clear silicone. In no time, the silicone attracts moss and lichen. If you try to get the moss and lichen off, you run the risk of 'damaging' the seal.
You really need to be working off a ladder cleaning those canopies, which from a H&S perspective, is a no-no. They will want you to tie off the ladder to the canopy frame and then wear a front clip safety harness tied off to the canopy frame as well. (Like the Sky satellite installers use.) The other suggestion is a short scaffold tower.
Depending on your course of safety action, then you need to add that to your estimate.
I'm guessing they will need to see proof of Liability insurance and I expect they will also need you to provide a RAMS (risk and method statement) document. This is why cleaning when the building is shut removes a lot of the risk involved.
