Machete is the best start. You clear the jungle quickly.
Spirit stone lets you clear faster and gives some regen for better survivability in the jungle.
The magic peneration from sorcerers shoes, runes, and your passive will make you dish out a lot of damage mid game.
The armor and health give you lots of tankiness that you need. This item also gives you tenacity which allows you to get something other than Mercury Treads.
Sunfire cape gives you health, armor, and a cool passive that lets you deal damage just by standing next to someone. Sunfire cape synergizes very well with Despair[W] because you will be dealing a lot of damage just by standing next to people.
Abyssal Scepter shreds magic resist like your passive. With all the magic penetration you have plus Abyssal Scepter, you will be dealing a lot of damage. The magic resist will also help you resist damage from AP Carries. The aura is very powerful because it increases the damage of the AP champions on your team.
Possible Late Game Items
Rylai's lets you slow people if you keep your Despair[W] on and walk next to them. Rylai's will give you damage and health, but other items would make you tankier.
Frozen heart is a good item when the enemy team has champions reliant on auto attacks.
If I need magic resist, I prefer to get
because it helps gives you a spell shield. A spell shield prevents you from getting silenced or stunned when you want to get in a good position to use your ultimate.
Randuin's omen makes it so when someone auto attacks you, their movement and attack speeds are reduced. This makes it so AD carries are scared of you because they can't auto attack you.
I hardly ever get this item, but it gives you a lot of damage and makes it so you can't get bursted if the enemy team is very strong.
I like this item, it gives you TONS OF DAMAGE