Painting breeze block
You can use a left over matte finish (I'm guessing this is what you were talking about), but the blocks will soak it up and you may need a few coats for a decent look. I would start with a masonry primer first that will seal and fill the pinholes, then you can topcoat it with whatever you want. 

You can paint the floor, but you're going to have give more information: Is it new concrete? Is it stained or sealed? Is it painted right now? Do you plan on parking cars on it? 

H&amp;C Shield-Crete and the Acrylic glaze to go over it may be your best bet.