Sorry this morning I was very tired, couldn't answer longer. So, we'll build a sandbag house with ecobeams, and according to the builder it has got a very good thermal mass. But I still wanted to check out the passive design, because we are committed to use as little energy as possible. One of our rooms where we currently stay happens to have a wonderful design( I'm sure accidentally
) where we get sunlight through the window during winter, and the room warms up very nicely, during summer it does not happen, so it's quite cool. I watched maybe a year ago Bill Mollison's Permaculture Design Course on DVD and I did remember that he was speaking about the % of the window surface, and the house design but I couldn't remember correctly. Since the post I've checked his book, and found some info, although not very much detailed.
So, thanks again for the answer!