Before installing the roofing material of your choice for the garage, you will need to install beams or decking, depending on the material. Timber flooring is used almost exclusively for asphalt roofing products such as roof felt or asphalt tiles. 

To find out the dimensions and density of the beams, you'll need to read the documentation at that comes with the timber roofing material – or even better, call a technician. 

If you need additional rainwater protection, you can install a plastic barrier just between the frame and the support beam. It is then nailed together to the beam. Be careful not to damage it anywhere as all holes will hit the target.

Once you have selected the type of roof shingle to place over the beams, the first thing to do is to place several small piles of shingles evenly on the beams. This allows you to carry out the actual application in a much smoother flow than if you had to get down the scaffolding to pick up the shingles. 

Whatever the ingredients, be careful when walking on them. Some types, such as slate roofs and clay tiles, won't like it if you walk on them. So try to avoid this. If you are laying asphalt tile, this will also need to be nailed, in this case to the timber.