You could also buy some cheap items in the beginning. Arcane Boots are a good way to go if you lack mana. Additonally to that you could buy Ring of Aquila (985 Gold) and Medallion of Courage (1075), which also lowers the armor of the enemy. Also useful for an early Roshan kill if your team goes for it.
That's 1450 for Arcane Boots + 985 + 1075 for the 2 items above = 3510 Gold. Also a good way to go if you play a semi-carry or carry role and get some farm. I'd also go for drums if no one else does. Next items are your choice and situational.
But with that above you should have some good mana reg.
In late game you do ofc sell those items, get BoT and items for damage, like AC/S&Y/Deso and stuff.