- Get some skate shoes - these can be any brand, really, but they should be big and puffy to really fit the look. Not all skate shoes look like this - in fact most don't - but stereotypical skate shoes look oversized.
- Baggy jeans - even though not all skaters wear that style, it works! Super tight jeans are also an option! A gross, disgusting option...
- A skater T-shirt - a shirt with a logo in the middle would work. Something like a skull. Skate shirts don't cost too much though, so you could get a real one. Or just take a plain white T shirt, and draw a skull on it. If you do a bad job, it will look more like a real skate shirt!
- A baseball cap or long shaggy ratty hair - again, not all skaters look like this, but a LOT do! You can get a wig, or an over-sized baseball cap, or both!
- A skateboard! This one is pretty obvious, and it might be the most expensive part of your costume. But, you CAN get super cheap skateboard knockoffs at Wallmart or Toys R Us. And this is the ONLY time you should EVER buy one of these! They cost like 10 or 20 bucks, and they are the most horrible skateboards ever made, but they will cheaply complete your skateboarder costume. Once you have it, take sandpaper to the bottom and grind off whatever picture is there. That will make the board look more real. And under no circumstances should you try to actually ride it. These boards are garbage, and they will try to kill you.
- Attitude - skaters traditionally have a sort of "screw you" attitude, so you can work on looking angry or hostile. Again, we don't all act that way, but there you go.
- BLOOD! - to complete you skater outfit, why not rip the clothes in a few places, and put some fake blood on your elbow, the side of your head, or anywhere, really. Put a few bandaids on your face. This kind of thing will really turn the whole outfit into a "costume", which is good. This way, also, if you are a real skater, you can just take old clothes and do this same thing with 'em, and BOOM! Costume! And it's not a far step to go a little further and make yourself into a zombie skater, or a vampire skater, or a ... anything, really. Werewolf skater? Why not! (You can get fake blood from costume shops)
If you really want to know how to dress like a skateboarder, because you want to be one and/or blend in, then read As a Skater, How Should I Dress? It covers the bigger questions, and gets more serious. But if you want a skateboarder COSTUME, then here are some ideas (by the way, if you are a poser and reading this, this stuff won't work for you to fit in with real skaters. Please, just don't try).
So, there you go. With these ideas, you should be able to build yourself a fun costume, and it shouldn't cost too much. Be careful, however, trying to wear this around a skatepark or other serious skaters - unless they have a good sense of humor, there's no telling what they'll think! For whatever reason you're building this costume, I hope you have a ton of fun!