The Self-Sufficient Living, AmazingRibs.com and TexasBarbecues.com provide plans to build a barbecue smoker, as of 2016. The sites have a wide variety of free plans that range from very simple construction to elaborate designs.
The Self-Sufficient Living has 12 plans available, including those constructed from cinder blocks, bricks and wood as well as construction designs from old barbecue grills and whiskey barrels. The designs range from small, single-meal style units to large, walk-in models. Smoking fuel options include wood and propane.
TexasBarbecues.com has several plans for constructing metal smokers, some of which require the user to have welding skills. AmazingRibs.com has plans for some elaborate brick smokers as well as links to many other smoker building resources.