I use DroneDeploy to create flight plans and create models. Limited access is free and there's also a free trial of the more advanced option. Model creation can get expensive after that if your models are large.
If you are doing intricate architecture then you may have to take additional low angle photos using a POI (Point of Interest) flight mode, in addition to those taken using DroneDeploy.
I am assuming you are using a drone - if so take care to investigate local regulations regarding flying drones, both generally and at the sites themselves.