Boxes are trickier than they look if you want to make them from scratch.  It can be difficult to get the lid to fit properly over the bottom.  I've made a couple, but wasn't exceptionally happy with them.

It is easier to start with an existing box, and then add papier mache and decorate it.  Even then, you need to let it all dry after just one or two layers because if it gets too wet, it will warp and not fit together when it is dry.

The cutest small box I ever made was made on a plastic pot with a screw lid that had contained face cream.  Everything already fit together nicely.  I just used PM to thicken and decorate the outside of the jar base and lid.

Sue

As you want a pot, I'm assuming we're talking about a cylindrical shape.  What I'd do is find a cylindrical form of the desired size (a plastic pop/drinking bottle), apply paper strips to it until you build up the desired thickness for the walls/bottom of the pot, and then let it dry before you remove it--you can also add handles/decoration or whatever to it as well.  For the top, take that same bottle, cut it open, and make a narrow paper mache strip ring from the INSIDE of the bottle (this will ensure that your pot lids fits inside of the pot proper that you just made).  Next, take your pot bottom, draw a circle around it with a pen/pencil on paper--that will make the shape for your pot lid--cut that out of thick cardboard stock, or something similarly sturdy.  You can build it up with more paper mache, if you like , or use it as-is, I'd recommend adding a handle though, so it's easy to remove/replace.  Now, getting back to that narrow, circular ring of paper mache we made from the inside of the bottle, glue that to the bottom of your lid, perfectly centered--that ring should make it so that you have a nice, tight fit for the lid on the pot.  Hope that all makes sense.

Also, I got this tutorial from a dollhouse furniture book I checked out from one of the local libraries a while back: