Veda Sereem describes the Oulid Nail costume in her video on Bou Saada.

Go to Google, click on Images and type in Ouled Nail, you'll get loads of photos from old post cards and a couple of new interpretations of the classic costume.

A key component of the Ouled Nail look is a crown-like headpiece or pillbox hat, with veils or scarves hanging down. A high turban decorated with a coin necklace could work. The scarves or veils should be sheer or lace (a single lace curtain panel will work)

Many postcard photos of Ouled Nail show them wearing chains from the headpieces, draped under the chin, like straps. A scarf could be worn the same way.

The Ouled Nail traditionally sent their daughters to the city to dance for their dowry, so coin jewelry is ideal. Large metal ethnic pieces will enhance the look and create a more traditional appearance. Lower arms are covered with heavy cuffs or dozens of chunky bracelets. The more jewelery, the better!! Put on too much, then add more. Remember, these dancers are wearing their entire life savings!

They wore long or elbow length sleeves and kept their bellies covered. They wore hip-length or longer tops, sometimes with short jackets or long, full coats over them. A "hippie" style top would work just fine, either by itself or over or under a caftan, beledi-style dress, or ghawazee style coat.

Always full harem pants. Sometimes a wrap or full skirt over the pants (esp with a knee to hip length top) An ordinary broomstick skirt works just fine. I like to slit the broomstick skirts so the pants beneath show a little more.

The tops, ranging from below the hip to below the knee, are worn over the skirt and/or pants, never tucked in. Many vintage photos show the dancers wearing these full tops with no belt at all. Some dancers wear a simple scarf at the hips, or a heavy, armor-like belt worn at the waist.

But I would suggest adding a decorative belt of some sort at the hips, to emphasize movements. Torso and hip movements disappear beneath layers of loose flowing tops and caftans. While belts at the waist are authentic according to postcard photographs, a belt at the hips works better for dancing today. A coin belt would be in keeping with the traditional style of wearing ones wealth, but tassel belts fit the image fine.

This link is from the bellydance museum. www.belly-dance.org/ouled-nail.html
with description how they looked.
en.wikipedia.org/wiki/Ouled_Nail with a little information.
www.youtube.com/watch this is an example of the music with pictures.
images.google.nl/images
For pictures search by google
www.youtube.com/watch A berberwoman on her weddingday


For a quick idea, a peplos with under a chemise. A pillowhat with coins, lots of coins as necklace.
Lots of kohl and henna.