For (mainly UK) layouts, 'PSL Book of Model Railway Track Plans', C J Freezer, ISBN 0-85059-905-9, published 1988 at £5-99. Over 70 layout plans, various scales and sizes.
Alternatively, look for and buy all back copies of 'Railway Modeller' published whilst Cyril was editor - he produced at least one detailed layout plan every month!
But don't try to make a Trainz layout the same size as the model - even a large one would be unlikely to fill even one Trainz baseboard! Take advantage of the unlimited space offered by Trainz to take a model plan and make it more realistic. See my web site* for my thoughts on the subject, and my layout 'Dukes Denver' (on the DLS, for TRS 2004 using only built-in assets) which uses, if I remember correctly, seven baseboards and is based on a CJF plan for 4.5 x 3.5 metres. * Click on Dukes Denver Designs, below.
Ray