How do you create a pyramid-like tapered incline?

[Anonymous]

I am trying to construct a 3D model of something that resembles a pyramid but has a continuous inclined surface that wraps around the outside until it comes to the peak.  Basically a square helix, but not open like a spring.  I hope that my drawing helps.

Tapered pyramid

[etfrench · Accepted solution]

With a square coil of course

[Anonymous]

Wow!  That's incredible!  You responded so quickly.  This is exactly what I needed, video and all.

Thank you.

Matthew