Not too long ago I saw a picture of a make it yourself, fold away workbench thing that had a secure vice atop it used to work on uppers and such. Since I myself do not have a dedicated workbench or vice and need to assemble an upper I was wondering if anyone knows what I am talking about and can tell me exactly what to buy at Home Depot today in order to make this thing.
 

If you send me the dimensions you want it to be I can make you a build plan for one. Pm me the specs and I'll get it to you this evening.

I've been thinking about doing this too. I don't have enough space in my garage to have a permananetly set up work bench

I appreciate it. It doesn't have to be any specific dimension, but "compact" in general. Fold away per say.

 

Get a Black & Decker Workmate. No man should be without one. With a little shimming and an extra c-clamp, you can install a barrel with the Workmate's jaws. If you want to be all proper like, you can mount a real vice to it by drilling some extra holes in the table top.

I made one just like this. The custom top replaces the work surface and it will still fold away. I only used it for reloading but it would be solid enough to build an AR.

Table

A lot of stand alone "work benches", folding or otherwise, leave a great deal to be desired in terms of stability/rigidity.  Permanent is best, but absent the room for that, if you can find a way to anchor your bench, you'll be much happier.  Nothing like having your workbench fold up under you or tip over while trying to torque a barrel nut on a several hundred dollar upper!

If you are not opposed to poking a couple small holes in your wall, you can build a simple work bench that will be quite secure, yet be able to store in the back of the closet when not in use.  If you have the ability to make the frame from steel, even better, but it can be done without.  

It's a simple matter of a top with two folding legs that use pins to keep them in the unfolded position (and folded, if you want), a couple of eye bolts in your wall studs, and simple wooden cams on either side to push out from the wall, tensioning the bench against the eye bolts.

You can also use threaded anchors in the studs if you don't want anything sticking out of your walls.  Then just use large thumb screws through a back splash on your bench.

I thought about doing this too, until I found out the WorkMate isn't made here in the US anymore, all you can get is a cheap made-in-china POS with the logo on it...nothing like the one my dad had and I abused for years.

I had the idea of mounting my vice to a large cable spool with weight in the center. Only drawback is the size of the work space. Wife uses one for gardening that has lockable casters on the bottom

Workmate. I picked one up at a yard sale, I use it all the time

I used this http://www.harborfreight.com/folding-clamping-workbench-with-movable-pegs-47844.html with a 4 inch vise. Just be sure to have a heavy toolbox on the bottom or something.
I secured the vise through the existing peg holes using bolts and washers so I can take the vise off easily and fold up the table.
Super cheap( $19) and good enough for this limited purpose.

My Workmate finally broke last weekend when it fell over while folded. Plastic piece holding on one of the lead screws gave out. It was a good portable work platform, but I can't see anchoring a sizable vise to it. A smaller vise with light service needs should be OK. That HF might be worth a look as a replacement.

Just buy a couple 2x4s and a sheet of 3/4" plywood, some screws and make yourself a saw horse type table. Bolt the vice on top of the table with either lags or predrill and use carriage bolts. I'd double up the plywood so that your top is nice and sturdy at 1 1/2" thick.