What to use to Measure Clouds
Make a Sky Window for observing the sky or use a mirror to measure cloud cover in eighths or 'oktas'.

You can use any largish mirror. Simply divide it into a grid with 16 equal squares using a ruler and a pen.

Using Oktas
On days when the sky is cloudy, take the mirror outside and lay it on the ground where you can see the whole sky reflected. Count the number of grid squares with cloud in them. Divide by 2 to find the number of oktas. O oktas is a clear sky. 8 oktas is an overcast sky.