This will be a step-by-step approach. You'll first need to sink two posts and nail a 2x4 between the two at the proper height (about 8 - 12 inches from the ground). This will serve as support for the bottom of the trough if a sheep goes nuts and wants to jump across or into it. The project pictured below have a plywood back because it's part of a building unlike my main feeding trough which is open from both ends (above).

If you need a roof above the trough to protect the feed from the elements then I'd suggest planning on putting full 8-ft posts in the ground. Once the posts are set, you'll be able to build an A-frame type structure using 2x4's and screwing (not nailing) corrugated metal sheeting to it. You can even place the trough between two beams on the side of a shelter if you pre-plan well; this is exactly what I'll be showing here since it adds a few steps.



From the Tool Crib you'll need:

Skill saw
Measuring tape
Level
Screw driver
          -better yet, a screwdriver bit and drill

Materials List:

Rough-cut cedar, dog eared used for fencing
Exterior/deck screws, course thread, 1-5/8"
Drywall screws, fine thread, 1-1/4"
Small piece of 2" x 4" thick wood (if needed)
 
1) Measure the width of the trough opening. Generally speaking you'll want 20-inches of space per animal otherwise they get a little more testy than they normally would otherwise. Do expect a little pushing a shoving regardless, especially from the rams. It seems that they're always at the back of the herd except during feeding time (go figure). 

Its best if the span between the posts is 4 - 5 ft (48 - 60 inches). Since my width here was 83-1/4" that means that I'll need to splice my cedar stock together since I only have 6-ft lengths. AS shown here, I'm having to make this trough especially wide because of this shelter's width.

Cedar is being used because it resists insects and doesn't rot; it's also inexpensive and commonly available.

3) Test fit the cuts by placing them in the opening. They should be the exact fit, perhaps 1/8" shorter than the opening. I test fit just to make sure I don't waste my time and need to re-build EVERYTHING all over again.

5) Once again, double check your work (Below) by putting the piece/s in place. It will help you see how everything goes together (Up to this point there are still no sides on this). It should also be noted here that the two sides (front and back of the trough) are of slightly different widths (about 1/2 inch) since they were overlapped when assembled.



7) As before, pre-drill the screws into the cedar before inserting the 2-inch pine. Mark or score the middle of the sides of the 2" pine as a guide during assembly. A sharpie or pencil are both good for this.

Fasten one side at a time so that you can clearly see the marks you just made.  

9) And for the third and final time, pre-drill the drywall screws into the cedar before inserting the sides and fastening them securely.

10) Using the exterior/deck screws, place the trough onto the 2x4 support and secure it to the posts using three screws on each side.

Being cedar, the finished trough needs NO painting, ever. Replacing and repairing it easily done by simply removing the exterior screws and inserting a new assembly in its place. So far, my first trough made in this manner has lasted about a year, was made from 15 year old fencing material from an old damaged fence, and looks virtually the same as when it was first built it (Shown at the top of the page). This was a new trough because this entire structure was made from new materials (I thought I'd spoil myself with fresh building material this time around)

Exterior screws are used when there is the possibility of rust developing. I've had drywall screws strip and/or break when they're old. The coating of exterior/deck screws should eliminate the problem.

2) Dividing my width by two(2), I cut my four pieces of cedar into equal lengths of 41-5/8". A cross-cut saw would have made better cuts but I was careful.

4) Since the fit was good,  screw the two pieces together to form a "V" using the fine thread drywall screws. I don't care if these rust because if these pieces need to be replaced later in their life I'll simply build an entirely new trough using fresh cedar. 

Take your time screwing these together. Pre-drilling the screws into the wood and allowing the point to pass through slightly will make assembly much easier for you (as shown). The points sticking through will act like push pins in the soft wood and keep everything aligned properly as you do the assembly. If you were for some reason wanting to use hardwood (expensive, but you can if you want) you MUST pre-drill ALL of the screw holes or else the wood will split.

6) I used a scrap piece of 2-inch thick pine as a way to join the middle of the trough. I placed the scrap in the groove and scored it with a nail then cut it with the skill saw. I placed it in the joint here in order to show how it neatly overlaps both sides of the trough.

 
8) Next you'll need to make the two sides (Below). If you've kept your trimmings you should probably have enough left over for this. Place the piece into the side, score it with a nail or pencil, and cut it to size. If you don't have scrap, look for a small piece of plywood or other material you may have tossed to the side as scrap.

You should have something resembling this when you get this far.

If you have a back-board (as I do here), additional screws will give added strength for those especially lengthy troughs.