I have a 5.8GHz digital cordless phone system (two handsets and base
station) that has reasonable range. It works fine inside the house and
within about 30-50m of the house outside. The house is steel frame clad
with cementitious planking and plasterboard lining, and has a steel roof.

Is it possible to improve the range of the handsets outside the house using
simple supplementary aerials or by relocating the base station? If so where
might I find design details?

I am competent with tools (I built the house) but don't know much about
radio.

David