Is there a way to make reasonably accurate visual measurements?
For a quick and dirty estimate, I'd try the following:


Take a camera and tripod as far away from the front of the house as
you can get.
Level the tripod and camera.
Take a picture of the full face of the house, zoomed in as much as possible.
Verify your scale:

Measure a few points on the house (windows are good, you can measure the picture and the inside of the window) on either side and different floors.
Make sure the scale of the picture at those points is consistent.
Note: they're not all going to be the same. Use the least favorable
scale for your estimates.

Assuming the scale is reasonably consistent, measure things on the
picture and multiply by the scale.
Add 10% (standard practice).


This works because you specifically wanted to overestimate rather than underestimate.  It will be more accurate the further you can get from the house for the picture.  I would never recommend this for construction work; but it should be good for holiday lights.