Building a bed alcove - any structural issues ?

[cbc58]

Was looking at the solar saltbox plans and really like the idea of a bed alcove in the living room. 

For existing structures - wonder if there would be any problems building one without a foundation under - with angled brace base supports.   Seeing as there will be the weight of the roof and person in the bed... would that cause any kind of 'pull away' problem on the structure?   

I realize the level would have to be raised somewhat to get some bracing support.  A picture of the alcove is here (4th & 5th pic)    http://countryplans.com/sb-tour.html   

Thinking of something 20"- 30"' off floor and maybe 4' tall with pitched roof.  Enough space for a bed with a curtain to pull for privacy.