How do you make a Luna Lovegood costume?

you can get a blue tie and use craft paint to stripe it with silver (you could even use duct tape if you wanted to be creative)

If you find a reasonably thick stick and strip the bark off it's fairly simple to taper it using a carpenter's knife.

You can find a good image of the Ravenclaw crest online and get some iron transfer paper, then iron it onto the lapel of your robes.

And, of course, you can poke wire through a couple of wine corks and wrap the ends around each other (make sure it's long enough to fit over your head) for the butterbeer cork necklace, And if you can find craft radishes, awesome, if not, just spray paint a couple of craft strawberries.

If this helps, great. I realize it's a bit after Halloween...

I was Luna last year for Halloween and it was very easy. I found a blue and grey striped tie, some sneakers and any kind of pants (or black pleated skirt) A white collared shirt, and a grey pullover sweater, with a black wizard rope or travelling cloak along with two handmade styrofoam radish earings. Me and my friend made wands by painting wooden spoons black and sawing off the end. My hair is already light blonde, but the blonde hair is pretty essential. If you want to go further, create your own quibbler magazine and offer it to people! And create your own wrackspurt glasses
Also, it is fun to use Luna quotes such as "Dont worry, your just as sane as I am" and use a dreamy voice.