The best place to do it is below the water tank.
In this instructables i will show you the way to do it.
2 Sheets of Wood.
A Dog or More
Step 1: Prepare the Area
Step 2: Cut the Wood Sheets
And cut the other one in accordance to the size of one the sides, this will be the entrance to the doghouse.
Step 3: Creating the Entrance to the Doghouse
Graduate the corners like coordinate axes.
To obtain a perfect curve the secret is to draw a line from the first grade (half centimeter) of one axe to the last grade in the other axe.
The result has to look as the pictures.
Repeat this in every corner.
Make a hole in the inside of oval with the drill to insert the handsaw.
Put the handsaw in the hole and cut!
Sanding the edge of the wood, you do not want your pet is injured.
Step 4: Make a PVC Tube Base
Then, with the aid of elbows and tees of pvc build a base.
This basis keeps your dog away from the cold and damp ground.
Step 6: Buildign a Doghouse
Put inside the PVC base.
Then put the other wood sheet.
Paint with the waterproof roof the insede of the lid which is the entrance. This is a good idea, it can be cleaned easily in the future.
Screw the lid to the base of the water tank.
Paint the outside of the lid.
Wait until dry.
Step 7: Stencil Style
In this case apply a stencil, stencil making is the subject of another instructable.
That's it, I hope your pets enjoy.