New to this, how do I prevent this image distortion?

https://support.dronesmadeeasy.com/hc/en-us/articles/207703746-Roof-of-a-building-didn-t-turn-out-well

https://support.dronesmadeeasy.com/hc/en-us/articles/207703736-Features-are-Distorted-or-Jagged

If you collect your data at 80% that number is only valid on the plane where you took off. Anything above that will get less overlap and anything below that will get more unless terrain awareness or a ground offset was used. 

This means that the roof really only got more like 77-ish%, which is still decent.

The real issue here is the metal roof is basically featureless and uniform while being somewhat reflective. This causes the feature matching algorithm to get confused and match inappropriate points. 

You can't do much about what the roof is made out of but you can take steps to reduce the presence of reflections: 

• Map during overcast conditions to minimize direct reflections
• Use a circular polarizer to cut reflections
• Map further away from solar noon to reduce reflective angles
• Collect extra overlap and manually remove images with bad reflections