As an electrician I must butt in here. You must do things by the book! There are rules out there for everybody's safety and for ease of work and your future expansion should you feel the need. It's great to come here and have all this free advice but there are some things that are missing:
1)Let us know what country you are in.
2)How long of a distance are you trying to connect.
I will never recommend running your cable in free air if you can do it another way. There are simply too many ways for it to get damaged.
It is correct to use rigid pvc conduit for buring cable.
1)If you are using direct burial cable it needs to be a minimum of 18".
2)It would be the same depth for PVC conduit so you should just use the conduit to offer your cables some protection from rot and damage.
3) It's cheap
Remember when installing any kind of wiring underground that there is no way to offer 100% protection from water intrusion whether it be in conduit, water-tight conduit, or even in concrete. Even the change in temperature will cause condensation. So use the correct type of wire that's designed for what you are trying to do.
LINE VOLTAGE CABLE (60 volts and up) AND LOW VOLTAGE CABLE CAN NOT BE RUN IN THE SAME CONDUIT! If your power cable were to heat up and burn, your LV cable would then become it's fuel. So don't do it.
Now some tips:
Keep your pipes as straight as possible and avoid having all your angles adding up to more than 360*. Even with just one cat5 cable you will need a mule to pull it through your whole run of pipe if more than 360*...trust me on that. Make sure you glue all your pipe connections! The glue isn't to keep out water it's there to keep the pipes from separating, even when buried underground. The simple friction from the cables being pulled through will separate the pipe sections. Avoid using flexible conduit for runs longer than 6'. It is very expensive compared to rigid PVC. It is also so soft that the cable will drag all the way and then you will need the mule again to pull it through unless it is arrow straight.
PLAN, PLAN, PLAN!
Make yourself a simple sketch of where your pipe will run and what you are going to need as far as length of pipe, angle fittings, and how and where your pipe will exit your house and enters your outbuilding.
Do a PDF search for a code book from the NEC. It has a the rules in it. You can also search for a NEC Handbook which is a little more user friendly. Use any of them from 2005 and up. I also recommend visiting an electrical supply store for advice and supplies, not your local Homey or Low big box store. They can usually steer you in the right direction and catch a mistake in your order better than a big box store.
I hope I was of some help and good luck!