You could get a 16" GSO mirror or buy a secondhand 16" lightbridge that the owner has found too heavy to cart around and use the optics. Not necessarily going to be the same as premium optics though.
"The Dobsonian Telescope" By Kriege/Berry is essential reading before you even think about buiding a big one. There are newer designs around that are lighter and more compact, but this book has all the principles that you need to know first.
