The following reference material has certainly helped me gain a better appreciation of Garden Railways and you might also find it useful. In no particular order:

"The Art of Garden Railways (Reaching for Realism)" by Ian Stock - a Garden Rail Special published by Atlantic Publications who also produce the excellent Garden Rail magazine. ISBN 978-1-902827-21-6

"A Garden Railway Adventure - Building & Operating the Southern Cross" by Nicolas Trudgian published by Garden Rail, Atlantic Publishers. ISBN 978-1-902827-20-09

"Practical Garden Railways" by Peter Jones and published by The Crowood Press. ISBN 978-1-86126-833-4

"Railways in Your Garden" edited by David Pratt & David Joy published by Garden Rail, Atlantic Publishers. ISBN 1-902827-01-5

"Garden Railroading - Getting Started in the Hobby" selected by Kent Johnson published by Garden Railways, Kalmbach Books. ISBN 0-89024-369-7

"Garden Railways in Focus" edited by Tag Gorton and published by Garden Rail magazine, Atlantic Publishing. ISBN1-902827-12-0

"Garden Railways - The Essential Guide to Construction" by Chris Hatton published by Noodle Books. ISBN978-0-9554110-4-5

"How to Design and Build Your Garden Railroad" by Jack Verducci published by Kalmbach Books. ISBN 0-89024-644-0 

"Greenberg's Guide to LGB Trains" by John R.Ottley published by Greenberg Publishing Company. Indispensable guide to LGB trains manufactured between circa 1961 to 1982 but unfortunately out of print.  ISBN 0-89778-091-4