Hey,
in some cases I don’t get a face when I connect lines. It happens when I’m drawing over an exploded image. I’ve created a little example. The lines are parallel to the correct axis (they are green and red if i change the color style to ‘by axis’).
What happens if you draw over an unexploded image? Why do you explode the image anyway?
Set the precision as high as it will go and then check the Z coordinates of all the intersections and endpoints using the Text tool. Are they all exactly the same?
If I don’t explode the image, the faces are created fine.
I explode the image because I saw this in a tutorial. It’s easy to draw over a floor plan: if the image is exploded, the walls get the texture of the plan so you can see where the windows are and stuff…
I would suggest waiting until after you’ve drawn the floor plan before exploding the image. this will make it easier to avoid reversed faces.
That happens some times. I think it’s one of those old bugs, that got stuck since the old versions.
For me, selecting all geometry and choosing Intersect Faces > With Selection works, sometimes. Other times I shift to Wireframe Mode > select all edges > Ctrl+X > Ctrl+Shift+V (Paste in Place) > And use the Make Face plugin to generate meshes.
Here’s a similar problem that I faced a long while ago:
Increase the precision as high as it will go. Use millimeters instead of meters, too.
OK. It’s not uncommon for users to be very slightly off axis which can create issues. There is a tolerance so that you can be almost on axis and still get the colored trailing line but be off axis enough to result in no face.
What Dave forgot to say is that you can avoid that particular problem by paying scrupulous attention to inference engine snaps.
Also the quicker way to trace over an image of a floor plan is to use the rectangle tool.
This auto-faces and since the two snapped corners are on the image it’s flat…
By over drawing and overlapping rectangles you can quickly get the room’s outlines.
A few added lines if needed…
After that you can do some judicious erasing to merge some outlines together…
thanks for the hint. In my case (and with my old floor plan and limited experience) it was easier to draw the lines individually 
hey slbaumgartner, I have no idea about the things you are talking about…?
The little markers and tooltips that pop up as you move your cursor while drawing. Scroll down and read the sections about inferences on this help page:
thanks for your link. I checked the video that was in the comments (ACAD dwg Import into SketchUp - YouTube) and it seems that this is solving my problem:
-select all
-intersect faces → with selection
I tried to reproduce, and it only happens when using the ‘explode’ on my floorplan. Maybe there is a better way to make the floorplan transparent so you can still see once you start drawing the walls…
You’re welcome. Yes, like I said Intersect Faces With Selection is one way to try to solve this issue. Glad your problem is solved.
And yes, there actually is a trick I use when tracing JPG floorplans. Parallel Projection > Top View > X-Ray Mode. 
