I was initially looking at building this A-frame design based off one I saw on the IPP Facebook page, but decided to build it a little larger and beefier. Nothing against that design and I know it has been successful for a number of people. Our boar is pretty large (~500 pounds) and the design I saw was too short for him to walk in and I had some concerns about the longevity of the design.
The base consists of two 4x4 pressure treated 8' and two pressure treated 2x4 8'. For the bracing in the front of the A-frame cut the 8' 2x4 down to 84 and 3/4", this will be placed at the entrance of lean-to and screwed into the 4x4's. Then cut your other 8' 2x4 down to 77 and 3/4 and then screw your two fence rail brackets at the back of your 4x4's so your 2x4 will be flush with the end of the 4x4's. Measure diagonally from corner to corner to make sure it is square and adjust as needed before adding the rafters.
Fence rail brackets for rear 2x4. https://www.homedepot.com/p/Simpson-Strong-Tie-FB-ZMAX-Galvanized-Fence-Rail-Bracket-for-2x4-Nominal-Lumber-FB24Z/100375311
For the roof you will want to get eleven 2x4 8' and cut ten of them for the rafters to 5' length with a 45 degree angle on each end. One will be used for the ridge board at 8'. Some of the excess you cut off will be used for collar ties to add rigidity to the structure.
I am sure there are tricks for putting the rafters and ridge board together and attaching them to your seal plate, but what I did was had my wife help me hold the ridge board level why I used a brad nailer to just quickly get everything attached. I then went back and screwed everything together with deck screws. Then I added hurricane ties like the picture below to six of the rafters, the rafters on the end I had to use different hurricane ties because of the cross brace on the front and back of the shelter.
Six of these hurricane ties.
Four of these hurricane ties.
Now we want to cut our collar ties from the leftover rafter wood. I placed mine approximately a foot down from the top. You can adjust yours as you see fit and cut to the length you need.
Here you can see the two vertical braces I made out of some of the scrap wood. You can adjust these to make whatever size you want your rear opening to be.
You will need four sheets of 4x8' 1/2" exterior grade plywood for the roof and rear of the A-frame. You will screw one full sheet onto the roof of each side making it flush with the bottom or top. Then rip one piece down to two 1x8' strips and screw one down to each side to complete the roof. For the back of the A-frame I just have someone hold the piece up to back and trace the outline of the A-frame and then cut it. Once I have that, I then have someone hold it to the back again and trace the outline of the two vertical braces where my opening is going to be. I cut right down the middle of the traced vertical braces so I will have decent overlap for the removable piece and the two end pieces that I screw to the frame. You can see that in some of the below pictures.
Rear door held in place with four window slide locks. This will help us gain access for cleaning or if a sows rear end is facing the back when farrowing in side. It can also get hot here in the summer, so I thought in the hotter months where it is primarily used for shade taking that off would allow for more airflow to help keep it a little cooler. We also paint the plywood on the back and the 2x4's in the front that are exposed to the elements to help protect the wood.
A-frame completed with galvanized roofing tin. I used four 10' sheets cut in half and then topped with a galvanized ridge cap.
View of A-frame with rear panel removed. Now that I am looking at this picture I probably should have painted the 2x4's on the rear of the A-frame to protect them from the elements when I don't have it closed up. Maybe later :)
Rear panel locked in place with sliding window locks.
I hope this post will be helpful to someone in building their next animal shelter.