A few years ago Glen Walker assembled a fantastic manual (in PDF) for building your own TARDIS, and it covers several methods for building the corner posts. You can download his manual through a link on Scarfwearer's site:
http://homepages.paradise.net.nz/~trekker/policeboxes/download.html
The above link is not Scarfwearer's site directly, but at Glen's request he would prefer people to access Scarfwearer's site (at least for downloading the manual) through his site, which is the above link.
I would also suggest checking out Scarfwearer's site, which is crammed full of helpful information on all aspects of building TARDIS replicas, especially consoles:
http://relative-dimensions.net/v2/home/index.htm
(Also, I hear that Glen has a revised edition of his TARDIS Builders' Manual in the works: no completion date set yet, but I'm anxious to see it!)
Dino.