Hi
I want to model a wall that it is curved at the top from both top sides.
I mean if i started from a plane i want the top two sides curved and the bottom sides the same ( 90 degree ).
How can i do it?
do you mean like a vault?
can you show a pic of whatn you watn here
might be easier ot help !
happy 2.5
IMHO, maybe you can use Bezier Curves to create the top sides, and use normal plane for the bottom.
I would model 1 section that looks like a tall skinny slice of bread. Then use an array modifier.
With a curve modifier for curving walls. (or not if you just want straight walls )
Easier than it sounds. Look for a tutorial on the array modifier.
It really depends on the geometry of the wall; angular flat wall or curved wall. Simple way to make the rounded top flat wall is to make it out from cylinder. Just rotate the cylinder so the rounded part is on its side. Erase bottom round half of cylinder. Select halved edge and extrude it down to form a wall with round top.
A picture would really help. 
perhaps the vault script?