I learn all cases,but for one thing i´m not sure. For example:
I saw the blue house. 
The blue house is Acusative case.
I understand that I saw the house is Ben evi gördüm
But i do not understand is MAVİ(BLUE) is changing with noun... Is mavi evi,OR maviyi evi?? 
That´s confusing me,because that´s like in my language....
Thank´s in advance..  

Turkish adjectives do not decline. As attributes they do not adjust themselves to the case and number of their main words. A very useful rule on all levels of learning.

If adjectives begin to decline they are not adjectives any more but they have changed into nouns. It happens also.

Teşekürler!! Andladım. ))))))))))))))))))))))))