A better alternative, advocated by others on this NG, is to buy a set of
round
drip trays that you normally but flower pots in. Assemble into a
vertical stack
(with rods), allowing a gap between each one, cut out middle of all but
the top
and bottom ones - to make a shaded but ventilated cavity - paint white
and you
have a homemade screen that should be food enough to sit in the sun and
not
'overheat'.. Apols for having forgotten who came up with this idea - I
remember
a link to a webpage. Hopefully he/she will respond later. That was a bit
advanced for me!

Here http://weather.overflow.net.au/station/stevenson.html

All the best
--
George in Epping, West Essex (107m asl)
www.eppingweather.co.uk