I have the book by Gervais, Home Recording Studio Build It like the Pros. And in it he proposes two different rooms, one that looks diamond-ish, but is essentially a square with 1/4th of it diagonal length chopped off and two outside corners on the front left and right side walls poking inward and one pentagram-ish with the front and left and right rear walls being equal length.

Are these rooms any good or should I stick to a rectangle with a good ratio?

I was thinking that the easiest thing to do would be a rectangle and just smack up some treatment on all the usual spots. But five corners lets me have more bass trapping. I am going to us a pair of Adam S3X-H as near/ midfields so the room has to be big, and I know that as the room gets bigger, the problem with modes gets smaller. I am a total noob on acoustics and I´m having problems taking in new knowledge (severe ADHD, still not medicated). For the rear basstrap I was thinking of having it twice the volume of the ones on the sides, plus doing the whole front wall a big basstrap, except for having the door there in the middle with diffusors on it in horizontal positions.

I don´t have a room yet but the ones I´m looking at are around 17x25x11-12 feet. I´m in a country where the labour is cheap, that´s why I wanna do something better and better looking than a rectangle

I´m looking for some pointers without getting too deep and technical

I am sure Rod has enough experience and techniques to make almost any space workable. Without extensive treatment though, I have found such orientations very dodgy. A rectangle with a great ratio is a bit more predictable. If you are building something or doing an extensive treatment, I suggest it would be worth your while employing a pro. Ideally a local, who's work you can hear and see. But it can be done long distance. Take a look here for some ideas.
John Sayers Productions
DD

Something like this is what I had in mind. I will make the room as big as I can. This project is sort of budget one, don´t want to spend any money on other than the material or labour.

Oooops. I love to paint