I plan to work with some building projects as a helper. However, they required to bring a hard hat.

Personally, I want the best of the best or the BEST bang for your buck when it comes to all assests from whistles to cell phones to TV systems to firestarters. So needless to say, I'll ask the same for hard-hats.

Is a hard-hat just a hard hat? Or should I be looking for something specific? In this area, I have absolutely no expertice.

They basically are all plastic domed hard hats. I personally prefer the ones with the all around brim since they help keep rain from dripping down inside of your slicker as in down your back. Otherwise, I reverse the headband and wear the hard hat backwards to improve rain dripping and visibility above eye level.

Get a white helmet (supervisor) and be impotent,,uh, I mean important!!!

Some worksites won't let you wear the hard hats with the full brims unless your ab iron worker (I don't know why) or they ones have the nice designs. If your going to a site that requires you to have a hard hat then they have to provide one, same with sfety glasses and all the other PPE except boots. But if you absolutely want the best hard hat get on of the Carbon Fiber ones but be warned they are expensive. If you do get the white one like wildman say's don't forget the clip board. I go out without my clipboard and every one wnts to talk to me when I have it they assume I'm doing somthing important and leave me alone.

Make sure the hard hat you buy meets the American National Standards Institute (ANSI) criteria. IIRC, its ANSI Z89.1. This can be found on a label inside the hat and allows the purchaser to acertain that the hat is appropriately impact resistant.

Back in the days I worked in the oil fields hard hats were aluminum (I guess plastic hadn't been invented yet). The best thing I can tell you is that a hard hat is pretty much designed to protect you from bumps on your noggin' if you happen to walk into a low beam or something. If someone drops an 18" pipe wrench from 90 feet up and it hits you, it is gonna do some damage, hard hat or not. Personally, if I had to wear a hardhat today I think I would look at one of the cowboy hat versions. Cowboy is cool ya know...

well if they fit the standard, they will provide adequate protection (if your looking at the right standard).

Good things to look at is the suspension of the helmets, the fit and comfort are importent issues.

When I used to actually "work", it was usually above the water and even above the land, which also subjected me to rather windy conditions.

I'd drill a hole through the back side of the helmet, near the lower edge, where I'd tie a lanyard and run the lanyard to a giant baby pin (made from a welding rod), that was clipped to my back belt loop. If the wind, or something else knocked my helmet off, it was not lost overboard, or cause me to climb down and take a walk to retrieve it.

If you work on hightst, there are helmets, that are designed for this use. They won't come of you head, even in the wind. They are usually designed from climbing helmets, but also comply by the industrial standards.

Drilling holes in a helmet can compromise the strenght.

This is the best of the best of the best:
Cowboy Hard Hat

Or there is this style...