Yes i do believe you are right, it would be a good idea to get frozen mallet in somewhat an early game seeing you want have enough life steal to heavily rely on it. How ever, i would exhcange it in late game for another bloodthirster for that extra damage amd lifesteal.

not bad over all but especially if your new to olaf this build could be hard for some people to play with due to the fact many people dont understand how to focus and farm but if they do that right im sure you do a lot of damage but if your intent on getting a lot of life-steal i wouldnt go 2 bloodthirsters and a starks id either go 1 and 1 or 2 bloodtirsters and a frozen mallet