Forgot to say aswell, An easy ark to make for porkers is to get 4 sheets of 18mm ply wood and some 4x2 timber.
Use one sheet as a roof, then cut two of the sheets into a near triangle shape, 6ft at the bottom 4ft at the top (to fit the roof) Build a frame out of 4x2 and fix them alltogether! easy peasy! You can then either felt the top or cover with corrogated sheeting, the whole ark is build in a morning!