Question: "How far can you cantilever a bumpout?"

Not far.

When you build a bumpout--a micro-addition to your house--you can typically either rest it on a foundation or cantilever it.

Cantilevering means to extend the bumpout into thin air.  No support posts (though this is an option, too).  It's an elegant look.

But it also limits how far you can extend the bumpout.

Image: (c) Lee Wallender; Licensed to About.com