How much would you bid a 12,000 Sq ft home with a pool ? To inspect
Way more info needed.
Casita or extra garages?
Outdoor kitchen or similar?
Many large homes have extra features or upgrades not typically found on smaller properties.
How much would you charge?
How many electrical panels? water heaters? space heating equipment? cooling? (5 central units instead of 1?) is it multi-family? how many bathrooms and bedrooms? how many kitchens? crawl spaces? basement(s)? how long would it take you to inspect? Some houses are big with large rooms, some have chicken size rooms with 100 systems and they take much longer to inspect. So it depends on the particular house (and how they are built varies with the area).
Adding to what Simon listed, you need to know your area.
Some locales have odd floor plans that take longer to inspect (multiple attic entry points, various roofing systems), others have clientele that have different expectations (more of an alert for you, not that it changes anything).
Report generation takes longer as well.
Click on the link and fill out the form. At least it will give you a ballpark number.
If you want a number, IMO nothing under $1600
Basically 3x4,000 square foot homes. Then look closely at detached or attached structures.
I would have been at $1,995.00 with the info supplied.