heeelllooo juco and welcome
not realy a practical idea as the weight on a ladder is not only down the leg but also your weight pushing the ladder back so your sections need to overlap by 2 rungs or so to give the strength so wood not a good option
you cant just stack one on top of the other as there will be no stability
have you thought about a combination ladder!!!
http://www.laddersalesdirect.co.uk/product_info.php?cPath=97_132&products_id=347...you could also build some stacking boxes from 18mm ply 2ft square by 18" deep
also if you want to pad out a step to keep a ladder level on stairs it needs to cover 2 steps [upside down L shape]for stability with the weight of the ladder central on the platform
with either heigh grip base or mechanicly fixed to the step
you can also get survayors ladders that are telescopic or 3ft clip together but are only desighned for light use like entry or decorating
http://www.loftsandladders.com/acatalog/Online_Catalogue_Telescopic_Ladders__Sur...