Drawing rectangle on existing geometry

birdhouse-roof rectangles.skp (267.8 KB)
Hello . Using SU for schools. Birdhouse on left each piece is separate group. I can draw a rectangle on it using outer corners of existing pcs. It works fine.
Birdhouse on right nothing in groups. When I draw same rectangle, using upper left and lower right corners like before, I only get partial or inner rectangle . This happens other student assignments and I can’t figure it out. Pls help me understand what’s happening. Mike

Make all groups

Check out this VIDEO Getting started with Sketchup - Part 4

thanks. I had watched it before but forgot. I relearned to Group elements first then draw rectangle on surface.
How is this different than drawing a door opening on a wall? If I draw wall 8’ high and 6" thick, and use bottom and left hand edge of the wall to draw a door rough opening, I get the door rough opening the size I want and pushpull works. I didn’t group the wall. What am I missing? thank you for your time.

Unless edges and faces are captured in a group or component, new ones drawn will automatically merge with them. So when you draw the rectangle across the loose (ungrouped) edges and faces, it gets broken up into pieces from where the merging finds intersections. If you draw an interior rectangle within a face, such as your door, it will split up the original wall face but since the overlap is total the new (door) rectangle won’t be split.

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Slowly seeping in. If stuff not grouped, new lines merge with the existing lines like my ungrouped birdhouse roof example. but it does create the inner portion of the roof since no existing lines there. Correct? Close? thank you.

No existing face there, but basically correct, yes.

Edit: it occurred to me after posting that there is another detail: when it finds a closed loop of edges, SketchUp will create a face to fill them. That’s why you draw a rectangle (which is four edges) but get a rectangular face bounded by those four edges. Or, in the case of your birdhouse, get the inner portion of the roof because the intersected edges form a closed loop around it.