I have started picking out the materials for this.  

Aluminum is a tad bit too expensive and not to great without a lathe.  I'm not going for tight dimensions, but I need a 6" diameter to do anything interesting.   I chose plain carbon steel for the base and top plate.  I'm looking to use 2 8" diameter discs 1/4" thick.  I got the steel from a local supplier.  I ended up getting a board ten feet long 8 inches wide for about $120. I have prepared one using a portable handsaw and an angle grinder .

I chose buna lip gaskets or l-gaskets to make the seal to the main chamber.  These end up costing bout 50 bucks for two at the 6" diameter.  A drop of Dow corning high vacuum grease will make a great seal.  The stuff is a little pricey for a whole tube but you can get 1/4 oz containers on ebay for about 5 bucks.

The chamber itself I'd like to be glass just over a foot high.  Glass is very inert has a low gas permeability and blocks UV light and x-rays that may come from experiments inside the chamber.  With glass it is important to be prepared for an implosion.  A shroud is an important accessory I recommend a sheet of lexan to be safe.  The glass wall thickness should be a minimum of 5mm.  This assessment is based on what I see out there in glass chambers.  I'd really like a reference that makes a recommendation based on ultimate desired pressure.  Wale sells some heavy wall 7mm thick glass  with a 6 inch OD.  It is about $200 for 5 feet shipped.  I do have a saw that can cut this tubing.  A tile saw will work.

Flanges are necessary to connect gauges, pumps valves and feedthroughs.  I want at least 3 flanges on each plate.  Blanks can be fitted when they are not in use.  flanges can be bought on ebay for less than $10 a piece.  They can be bought as blanks or adapters and brazed onto the chamber.