Should I Be Concerned About This Roof?

[zoning-clang-spilt]

I'm considering purchasing this property in Cheshire and would appreciate professional opinions on the roof condition from this aerial photo.
Specific questions:

1. • How serious is the biological growth/staining visible?
   • Can anyone identify the approximate age/type of these tiles?
   • Are there any red flags that warrant a detailed inspection before purchase?
   • What maintenance costs should I budget for in years 1-5?
   • The darker tiles - are these replacements indicating previous issues?
     
     Would you recommend a full survey before proceeding? Any specific things I should ask a surveyor to check?

 

[Deluks]

Looks alright from here.

 

[catlad]

Birds sit on aerials and do their business, which then feeds the growth of moss.
Nothing to be concerned about.