The layout began in February 1998, and I am still working on it.  My trains had not been up since 1986 and I wanted my two teenage daughters (13 & 14 years old) to see them again. The trains are now permanent in what was once called the "dining room."  We never ate in there anyway! 
The 7'x'11' layout is 41 inches high.  The plywood top was covered with green indoor/outdoor carpeting. I used 1/4" sheet cork, hand cutting it with a beveled edge for a ballast base.  This was covered with Durasorb brand absorbent granules used in auto shop floor clean-ups.