Combine all the techniques.

1. Go to the plains. Find one of those colossal stone pillars on top of a hill.

2. Build on top in stone reinforced with iron poles as high as possible.

3. Switch to wood to build higher. Wood placed on red stone will be blue allowing you to go up from there.

3a. On or near the top, build a portal paired with one at the base so you don't have to physically climb the damn thing every time you go up or down.

I have never tried this (yet). I wonder if you can get it so tall that the top won't even render in from the base.