My first venture into hops tower construction is a charming, if not entirely stable, design. Its main advantages are that it's dirt cheap and very easy for one person to build quickly.
These are the hops towers at my current place of residence, the Butz Barn. I built two last spring and three this spring, and they've all done quite nicely. However, the first hops towers I built in this fashion were at my parents' house, which gets quite a bit of wind in the back yard. Those towers lasted for about a year before they started falling over---the bamboo would snap under the pressures of wind and hops. Not fun.
This is a design that I would say is fairly sound as long as you don't have too much wind in your yard, and have some good, sturdy bamboo. I salvaged all of my construction bamboo from the curb, from neighbors who grow it ornamentally and occasionally cut it back. One neighbor's bamboo turned out to be brittle and not very strong, another's bamboo has been quite reliable thus far. The towers that broke and fell were all built out of the more brittle bamboo. So, for this design to succeed in the long term, the quality of the bamboo must be very high.
The principle is very simple. Tie three bamboo poles together just below the top, then bury them in the ground like a tripod. This gives each of your three shoots (if you've been a good hops grower and pruned your shoots!) a path to climb upwards, and the tripod structure keeps it fairly stable without too much effort.
I tie the three poles together at the top before putting it in the ground, because that way it's freestanding, and I can position it correctly myself before burying it.
It's best to build this before planting the hops, because not only do you not have to worry about interfering with the hops' roots, you can also just dig one big hole, place the tower, and then add compost/mix the soil for the hops, then plant the rhizome. Otherwise, if you're like me this spring and kept putting off building new towers, you can just dig three holes around your hops, keeping a fair distance so as not to disturb the rhizome. Wider is better, since it will make the structure more stable. You can see in the pictures above that I have not followed these rules. The Butz Barn backyard is shielded by other houses, a garage, and a forested area, so we pretty much never get wind there---stability is less of an issue.
When these start blowing over, it's time to look at Hops Tower, Mk. II!