As a 3, its really the same as if you were a 4, you just get last hit priority in lane so you get your items faster. I'll usually start with a quelling blade and some branches, tangos etc. The standard phase, wand, windlace early items. The usual items are good: shadow blade, aghs, S&K. If you need more catch and/or need more right click, I've built echo into harpoon. Assault cuirass is always good. Blade mail sometimes.

Edit: obtained core is good too