How do you build a Gmrs/Frs radio amplifier antenna

[johnson 2]

I have a extreme problem with this, I have a pair of two way radios that do not have an external antenna output, so they are not moblie they are handheld type. Now I really would apreciate if you guys could give me a link (In english) on how to build one for handheld units because i can not find one.  For a verticle one like 1/4 wave what materials do I need and how do I build one. PLEASE give details PLEASE