Last minute issues

I'm so close to finishing the modelling process now and I have been checking over the models for their scales and I have found a small issue that will need addressing now before I go onto the unwrapping and testing stage. I have tried to keep all objects within a 256x256 pixel block so they are functional modular pieces. However I have just noticed that the wall pieces are not flat on the factor of 16 grid plane. A small print screen here shows this.

Here I have highlighted the issue with the walls each grid space is 16 units and is the scale I've used for the whole model space. The red line shows the centre point of the current wall piece, and the blue line is where the centre point should be for this to work.

The solution for this could be that the wall piece's pivot point be put on a factor of 16 which can be seen below. The green cross marks a suitable location for the pivot, this should hopefully also work when the wall is then rotated back around 180 degrees.