kalnins2003 This is not a roof but a shading screen. To make bamboo roofing waterproof you can do it with bamboo poles cut in half an placed them in a similar fashion as clay roofing tiles - the U shaped half pieces with legs up are covered with upside down pieces to cover the joint.

Bamboocreasian As we can see on the photo, in order to make roofing you should choose Quality Roll Bamboo Panels. Please click this link : http://www.bamboocreasian.com/bamboo.html
Selection of quality bamboo fences made from the most durable and straight poles which are harvested at least 3 years old to get old enough wall thickness of bamboo poles to not absorb moisture and water. Each panel is connected through a series of galvanized steel wire (Bamboo poles are threaded together with galvanized steel).

Used for: Roofing, Walls and ceilings covering , Build tiki bar; bamboo tiki hut…
Other Sizes: 4ftx8ft,6ftx8ft,7ftx8ft,8ftx8ft, Colors: Natural, Carbonized, Mahogany from 1/8”dia. ¾” dia, 1”dia to 2”dia available.

As olldbobbi 's answer: Waterproof solution, you should paint Drylock or Thompsons Water Sealer.