OOP and top-down/bottom-up design

I'm starting to get into OOP with sepples.

Since OOP came to exist because of programmers getting lost in their code, OOP tries to clear it up.
I came to a conclusion that OOP and design documents are vital for me getting serious in making large projects with sepples.

Thus OOP, top-down design and design documents go hand in hand.
So, how would I go at designing my project in OOP/sepples?
(And any neat software out there for making a design document?)

>>8
Abstract concepts don't have hands.