You will also find neutral buildings dotted around maps. The Goblin Laboratory, by way of instance, can sell a Goblin Shredder, which is very good for wow classic gold collecting substantial sums of lumber in a short time. In addition they sell Goblin Zeppelins, making excellent scouts for recon. These neutral buildings are frequently guarded by creeps. Should you just happen to need something from a neutral construction, however the levels of this creeps surrounding you're too high, try waiting for nightfall. Creeps sleep at nighttime, so you can rush in and rush outside without a danger!
The early game in any match is all about speed and efficiency, as well as fielding the most effective units possible, whenever possible. With different buildings dedicated to resources, tech trees, units, and defence, it's worth having a construct order in mind so that you don't get overwhelmed.
Much like heroes, it is hard to give a definitive answer to what you should prioritise on your build order, since there's so many factors that could play into your overall strategy. Nevertheless, when you're first beginning, there are a number of generally agreed upon strings that are worth studying, if only to use them as a template for your own. Nailing the nuances of aggressive Warcraft 3 has been a years long iterative process. You will likely find something new every time you play, watch, or even read about a game.
As a final bonus tip, be sure you spend two minutes repeatedly clicking on every unit until they get annoyed with you and cheap wow gold classic start spouting hilarious dialogue. This is widely considered to be the most important part of Warcraft, and it'd be a crime to miss out. Happy zugging!