Fatih,
I'll be sending you pictures of how to build both a bio and mechanical filter very soon, but the shape of your tank and the fact it doesn't have a center drain is not optimum.
That said we all have to work with what we have, and you can make it work if you don't mind vacuuming out some settleable solids.
Just set up my fourth high school system and we're adding on to the house so I've been a little busy.
What is the height of your tank and do you have access to plastic barrels?
