In a sketchup project, I select RECTANGLE and size it roughly to length. I then use the PUH/PULL tool to get a depth and make a joist. Then I use the ARROW tool to group all the sides together. Now I select the end face and use the PUSH/PULL tool to resize the length of the joist I can increase the length but not shorten it. What am I doing wrong? Also there are seven other joists on this sketch which were copied from one. But this new joist is being created in an unattached area on the sketch.
This sounds to me as if the face you are trying to work on is not perpendicular to the length of the 2x6. Or at least one long side of the 2x6 is not perpendicular to the end.
Upload the file so we can see it and give you an exact answer.
Out of curiosity, why are you only sizing it “roughly to length”? It would be easier and less work to create it at the exact length required. It would also be easier to model it in place.
if you use the ‘Select Tool’ [arrow cursor] and group the sides only, they are ‘protected’…
make the group after you push/pull to all the sizes you want…