Question: I hope this isn't too broad.

I would like an Earth-like planet for November's [NaNoWriMo](http://nanowrimo.org/) that is just enormous, but plausible.

Then I started to get into material composition, proximity to the star, trying to achieve the right densities - well, you get the idea.

I'm trying to have 10x the radius of our current Earth, but with similar gravity (ugh) and at least somewhat similar climate and surface conditions; I do not need to have life on this planet, but minerals and liquid water are important to us. Not quite a Jupiter-sized planet, but much larger than ours. Other factors can be modified.

Answer: 
Let me say it outright from the start: you can't get a $10 \times R\_\oplus$ radius world to be inhabitable by anything resembling humans.

Before you despair, let me remind you that planetary surface increases with the square of the radius, and Earth is huge to begin with: 510 million square kilometers. So for twice the radius, you get 2.04 **billion** square km, and for three times the radius, you get 4.5 billion square km, nearly 10 times larger!

Imagine how different history would have been had the Earth been that large. The larger surface area might mean slower days with longer nights, or perhaps faster orbital rotation. The terror of the night would be prolonged, or storms might be more massive than anything we know here on Earth. The vast oceans would regulate and moderate climate more than on Earth with their vast heat capacity, while waves might build up over the ocean vasts to truly astonishing heights (100m or more). The atmosphere itself would likely be deeper and denser, and given the higher planetary mass, retain more of the primordial gases.

**So how do you get such a thing?** The most likely process would be to start from a [Chthonian planet](http://en.wikipedia.org/wiki/Chthonian_planet), have it drift away from the star and rebuild some of the atmosphere from comets and eruptions.
Magnetism is "stronger" than gravity, right?

So what about an artifical planet with layers of nanite-controled magnetized iron (combined with sort of forcefield) that holds thicker layers of rock, many with air and water on them?
The planet is divided like an onion or a spherical sky scraper, many layers have life, perhapse from different planets.
Carefull use of nanomachines is how the magnetized mega-structures were made in the first place.