I have a stacking plastic worm farm but it was never much of a success, partially due no doubt to lack of attention on my part but the worms never seemed to do very well and anyway I needed something bigger. After reading "Organic Growing With Worms" by David Murphy, I liked his design for a "neverfill wormery" but it was all constructed out of "Ammoniacal Copper Quaternary" treated timber, and at about $1.60 per linear metre (well the stuff that I found was) it would have been a very expensive worm farm, and contain very little recycled materials.
I had intended to site the bath between the new greenhouse and the first veggie patch, not ideal because the site was very exposed, but the space was there and it was accessible. Then it occurred to me that I should construct it inside the second "goat" shed. There are two well ventilated sheds against the north fence that one day may house a goat or two depending on lots of factors, but I would like to have home produced milk and cheese. One is currently the deep litter chook shed, the other is untenanted (except for the spiders!). The worm bath is very sheltered in the shed and if I ever do get the goat(s) I won’t have to transport the manure very far to compost it. Having decided where to site the bath I then made a support frame of 100 x 100mm oregon timber left over from the veggie patch surrounds and then dragged out the bath.
The bath itself was an old Malleys one, it was a short one at 1300mm long all up rather than the more conventional 1500mm or so long. It is of the standard enamelled steel construction bought for $25 from a local recycler.
The original design called for one row of slits around the bath for ventilation, but I put in three rows all the way around the bath because of the importance placed on getting gas exchange by David Murphy. I also made no provision for harvesting the leakage (the so called "worm wee") because in David’s book he argues that it rapidly becomes anaerobic, smelly and unhealthy within a week or two so is useless. He says that the liquid manure should be made by dispersing mature worm castings in water. Taking this into account made the job a bit easier because I was trying to work out a way of getting the worm wee out easily, now all seepage and be absorbed into the ground directly below the baths’ plug hole.
Before I could set it up I had to make the cuts in the side of the bath with an angle grinder. This is a fun job that is noisy as buggery (not to be contemplated before midday on a weekend lest your neighbours lynch you!) and emits showers of sparks that HURT if they hit unprotected skin, but are entertaining to someone watching you from a distance. I put in three layers of ventilation slits, about 45 to 50 all up, and went through about half a dozen disks doing it. The 100mm angle grinder also got mighty warm so I had to have about 3 bites of the cherry to get it done. The warmth may have been because the angle grinder (like me) is getting on a bit, but it was a fair job of work to do.
Once the bath had been cut and was set up in the shed, I put in about 30mm of gravel over the bottom for drainage, I used crushed terracotta as the gravel but I am sure almost any kind would do. Just before doing that I put a small piece of sarlon over the plug hole to prevent the gravel going AWOL. The gravel I then covered with sarlon (better drainage than weed matting) to separate the worm castings from the gravel. 
Then went in a layer of shredded paper obtained from work and then a layer of broken down straw and chook poo from the deep litter shed. Both materials were soaked with water first by placing the materials in a wheel barrow, spraying them water from one of the tanks and mixing and massaging the materials in the water by hand. 
Finally a layer of cow manure was placed over the top. I picked up 1000 tiger worms from a local supplier and placed them on top of the manure layer and they seemed very happy to dig down into it. It was finished off with a sheet of wet hessian sacking to keep the top of the bath moist and give the forms some protection when they come up to the surface to feed.
Here's what it looks like after couple of years continuous use.
I feed the worms about once a week, during the week we save up veggie scraps and peelings and over fruit and veggie waste in the freezer, I then thaw them out on Saturday and feed to the worms. The freezing starts to break down the cell walls, making it easier for the worms to ingest. I only put the feed on one half of the bath, harvesting the other side to make seed raising mixture and potting mix from. Once one side is exhaused, I fill it up with cocopeat and move the feed over to that side. Give the worms a week to migrate and then the worm castings are ready for use.
