There are few item builds on mortred , its hard to say which one is best.
First one is most common one in 'skilled' games :
PT , basil/poorman's shield / stick / battle fury ( or rush midas then fury) , and later Helm of dominator/bkb/mkb
Second one is not used so often, but it can work as div.ide mentioned:
pt basil stick > vlads > desolator > bkb etc
And third one, most underrated one :
Phase, stick/poorman's shield , (vanguard) , yasha , basher > abyssal / bkb
It all depends on your game and your goal in it, if you want mass farm you choose 1st build, if u want to get fast towers with your team and still be useful late, you get 2nd , and if you dont have AoE potential in your team and you are 'one-by-one' killers, 3rd build rapes hardcore.