Diagonally positioned tiles create interest on a floor. However, be prepared to have a lot more waste than if you were to place them parallel to wall. Before you decide how to install the floor, consider the overall look, feel and style of your interior. Tiles installed at a diamond orientation communicate more of a classic, traditional interior than the parallel method. It is more a matter of aesthetics than anything else.

Mohammad. I understand your program. You may be lost in the details at the moment. Please do follow and trust the advice given here by all these people. You are about to embark on a reasonably expensive journey. Get professional help with someone who you can sit down at a table and brainstorm with them your ideas and intentions. There are Architects and there are professional building designers who are members of the American Institute of Building Design (AIBD) who are well versed in projects such as yours. I personally love a design challenge. After 38 years designing homes and special use buildings I enjoy this type of challenge the most. I am in Ohio and may not be close to where you are but I am sure with a little investigation you will find the best design professional for you.

Firstly, one can play a lot with furnishings if you are staying in a rented apartment. those white walls are nothing but a clean canvas and you can really use colors through your furnishings like cushions , upholstery, curtains , rugs etc to add colors . Secondly , instead of wall shelves etc add small side tables on emptycorners you get etc which gives you platform surfaces to display your nick knacks.. You get many freestanding display shelves online and in market where you don't have to use screws in wall. :)

You have to post as many pictures to help anyone figure out how it looks like :)