ALWAYS Brutalizer first. Boots when theres leftover 325 gold, but not too late since you need the speed. Avarice blade is required early for the gold income. Ionian Boots should be purchased when you have brutalizer and avarice, followed by the parts for Last Whisper. Depending on how well youre doing, buy tiamat (if you have around 1900+ gold), or BF Sword (if you have around 1600 gold). After having both Tiamat and BF Sword, get around 1900 gold, and upgrade avarice and bruta into youmuu, and buy another brutalizer. From then, just upgrade to Hydra (1400g), BT (1950g), and Cleaver (1663g).

About the situationals, buy them according to the enemy team (spirit visage instead of bruta if theres a lot of magic damage, thornmail instead of BT if theres Yasuo or something).