Don't mess about with lasers, that's a big boys toy in a properly constructed cloud base recorder only to use by trained chaps.
The easy way is, if you have access to both surface temperature and dew point, is to calculate the cloud base using that information.
In the International Standard Atmosphere, air cools from the surface up to 11000m at a rate of 2 degrees per 1000ft.
i.e If the tempertaure is 06 deg C and the Dew Point is 04 deg C, you can expect cloud to start forming at 1000ft.
Not entirely a precise science, but close enough for Government Work (and big boys).