In our pamphlet we said: "Build your own Poo Garden in 8 simple steps".
So our plan was to use the pamphlet and follow the instructions as close as possible, to put them to the test.

1

Gather materials to build a planter box.

Our first step was to change the basic layout from a single toilet in a square box to a his&hers double toilet in an oblong box.
That was because we were lucky and didn't have to build a box, but got one as a present from our friend Tim "learn how to think out of the dumpster" Anderson, who saved a lot of transport crates from a garbage pile. So: first thing we learned while building the prototype: look for occasions to reuse boxes, there are a lot of wooden transport containers, that are usually thrown away. And using them saves a lot of time, work and energy compared to building a new box out of pallet wood.
So we should change the first line: "Find or build a planter box". And add: "Square boxes make a good single toilet, oblong boxes can be used as doubles with two toilet seats positioned back to back."
The size of our box is about: 3 ft wide, 8 ft long and 3 ft high.

2

Building box, building soil, prevent leaching

To prevent leaking, first we lined the box with a piece of tarp. We filled in some cardboard, soil, woodchips and straw to cover the bottom.

3

Assemble a platform for the toilet seat

For the platforms we used two pieces of plywood, 
To stabilize the platforms we mounted them each onto to two two-by-fours. They are wider than the box, because we want to be able to move them to other planter boxes, that might be wider than the actual one. (That is the main point in our design: build the mobile seat and a mobile screen for privacy and be able to use uncountable numbers of random boxes temporarily as toilets and then use these Poo Gardens to green the world. So it is generally important to build the platform and the screening as flexible as possible, so they can be used in diverse settings.)

We used drill and jigsaw to cut holes into the plywood, size of the holes is a little bit bigger than the size of the hole in the toilet seat. Find out the right place for the hole: it depends on how thick the edge of the planter box is. The closer to the edge you can mount the seat the more comfortable it is to use.
Then we mounted the toilet seats. Important to keep out flies: find toilet seats that are as flat as possible, we want no gaps, neither between seat and platform, nor between seat and lid. We removed some plastic spacers and used window stripping to seal the remaining gaps.

On the bottom layer of soil (and compostable materials) we placed to big cardboard boxes as poo compartments. We put them in a little slanted, so that whatever in there - ;) - can slide towards the end of the box.

4

Buy or make a urine diverting toilet seat.

We build the urine diverting toilet seat by simply screwing a funnel to the platform in the front part of the hole. Seems to work pretty good and saves 117,- $ compared to buying a urine diverting toilet seat.

5

Drill a series of holes around the top half of the bottle, drill a hole for the hose.

The holes for urine dispersion can be drilled with a normal 1/4" drill, for the bigger holes (to insert the irrigation tubing that will connect the urine diverting funnel with the dispersing bottles) we use a holesaw of the same diameter as the tubing. A holesaw is a kind of a drill bit with a circular serrated edge, that cuts perfectly round holes.

6, 7

Connect urine diverter with bottles, place the bottles.

We measure and cut 4 pieces of the irrigation tubing each appx 3 ft long, connect them to the tees. Then we fill in more soil, cardboard and straw to create the bedding to put in the bottles. Directly around the bottles we use woodchips, because the pieces are so much bigger than the holes in the bottles, that they can't clog them. To be sure that the urine gets dispersed fast, without any congestion we put a tee-piece to the funnel, so two tubes for each funnel transport the urine to the bottles in the mulchbed. The funnel with the tee is placed in front of the cardboard box, the irrigation tubing leads on both sides to the middle part of the planter, the bottles are located between the two cardboard boxes.

8

Raise the flaps of, tap a skirt around the box.

We put the cardboard boxes in sideways, so no flaps to raise …

Attaching the paper (we just used brown wrapping paper) was a bit finicky, hard to reach the front part. Next problem that occurred: the weight of the soil we added later to fill the rest of the planter box ripped of the paper and after the first rain also dented the cardboard boxes. We added plywood backwalls to our privacy booths, to keep the weight of the soil off these fragile parts.
Note also: these toilets are created to be used and filled up relatively fast, of course the cardboard boxes will collapse sooner or later, and they are supposed to do that, as a part of the composting process that follows the use. Keeping this idea in mind, we avoided to use any non-compostable materials inside of the box (exept the lining tarp). The skirt around the opening of the poo-box is paper, and we also used paper tape.

This part of building the Poo Garden was done relatively fast: one afternoon for building the platforms with the attached toilet seats, next time lining and filling and attaching funnels to platforms and platforms to planter box. And then the next time we worked on it, we were able to finish the installation and under the veil of darkness we inaugurated our first dry composting toilet Poo Garden.

Building the privacy screen took a bit longer… due to the harsh winds in Alameda, where we built the prototype, our market umbrella idea was not functional. We ended building two outhouse-like booths, with roof.

Gathering the materials was a thing we underestimated. It can take a long time and it's annoying, if you have to interrupt the building for buying one special part because nothing fits. And then all the hardware stores in the area are exactly out of these little parts. So the most important conclusion of our prototype-building would be to add a material list.
Note: During rainy season it's good to be able to control how much water gets into the "filled" Poo Gardens. The soil part should not get too wet, you don't want overflow and also not too water-saturated soil.

Materials, tools, good to have

You need:

- 1 box or wood (+other supplies) to build one

- tarp, big enough to line it

- big and stable pieces of (ply)wood to build platform

- funnel

- tee in the fitting size

- tubing to connect tee and funnel

- tubing to connect tee and bottles ( xxx ft)

- two soda bottles

- tape

- (butcher) paper for skirt

- weather stripping for windows or doors: choose the thick and wide type

- piece of wood to attach to back side of platform to keep pressure off skirt and cardboard box

- soil, woodchips, straw, mulch

- cardboard boxes

- cardboard

- plants

Thanks to: Tim, Yuki, noisebridge, Spring, Timbo and Nik