Can someone take a look at this file and tell me what I’m doing wrong? It printed fine until I made a couple small changes and now when I try to print it, whole sections aren’t printing. Thank you for any input.
Fireplace 9 Case.stl (80.7 KB)
How about uploading the SKP file, instead?
There are reversed face.
There are edges that will cause a problem because there’s no thickness at those points.
And there’s a bunch of internal faces that need to be removed.
I cleaned up the internal faces and the reversed face. Then I added a little thickness at those locations I circled, above, and not it shows as solid and should be printable.
Wow! Thank you. I’m trying to fix all those errors you pointed out, but I’m fairly new to sketch up and it’s taking forever. 
Would you be cool with sending me the sketch up file that you fixed?
Here you go. Look at it and compare it closely with your model so you can see the difference.
FWIW, those bits where I added in some geometry to get rid of the zero-thickness areas may not be exactly what you need. It may be that you need to revise them. Or maybe it makes more sense to 3D print it as is and then file away some of the material there.
Fireplace 9 Temp.skp (202.5 KB)
Thank you, Dave!