Hello!

So far I thought the expression of having with the word "sahip" must be always accompanied by the verb "olmak", for example: B´e sahip olan A = A which has B. However, recently I´ve came across an expression without olmak (it was in my Turkish phrasebook): (...) kapasiteye sahip bir odanız var mı? Could you explain to me when it is neccessary to use "olmak" next to sahip and when it is not?

sahip is an Arabic loanword which means ‘owner’. Take it as any noun. As you know in noun clauses ‘to be’ is inflected to the noun phrase as an enclitic suffix.

Her doğan çocuk yaşamak hakkına sahip|tir.

You need to ask the verb olmak for help in two cases:

1. When you have necessary grammatical markers in your hands and you need a verb root to attach them to.

…nükleer teknolojiye sâhip ol|ma|y|an devlet…

…Facebook´a sahip ol|duğ|u|n|u sanan kullanıcı hakkında yanlış bilgiler… 

2. When there is the meaning of change, equivalent to the English become (‘to become the owner of something’ ).

Bu eve sahip olmak ister misiniz?

It is a little confusing that a dictionary gives sahip olmak for ‘to own’ but you have to know a great deal about the verb ‘to be’ before you can use it correctly in every situation.

(My Try.)