Usually when I use the mirror modifyer, it duplicates and flips the object 180 degrees along whatever the axis i choose it to be, but for some strange reason, it only tilted it 90 degrees. How would I fix this? it worked fine with the part part of the window, but not this one.
Main thing I noticed is that you have the width of your model in the Y axis. Mirror mod defaults to X axis for mirroring but you can tell it which axis to use. As a general rule you should try to orient your model to point along the y axis, with the x axis as the width. So you can use options like x axis mirroring in edit mode and pose mirroring for armature animations. Its just a good practice to get into.
Check the object rotation and scale. If it has unapplied rotation (other than 0,0,0) or unapplied scale (other than 1,1,1), modifiers and tools might behave weirdly. Ctrl+A to apply.
