Error with Mirror Modifier. What did I wrong?

[spoonetti]

Hi there, just a short question. It's not about TMT though, but I hope it's ok to post it in this thread anyway

In Blender I've started to create a roof for an old German fairy house. First I've created just one side of the house and wanted to add a mirror modifier. But something went wrong. The mirrored half is overlapping.
Could anyone tell my what i did wrong? Has this possibly to do with the rotation and scale settings which I was adjusting first (-90/180/180 and scale to 100)?

Thx for your answers!

 

[Samplerocker]

it seems that the origin point is not 0/0/0

also you could move it to the side and check that you don't have logged "do clipping"

also its possible that you have to switch the visual point not to the object and setting it to cursor. Then the curser must be at the origin point.