As said: only copy one level at a time . In project1 make only one level visible and select everything with ctrl+A. Copy and go to project2. Make sure the level you want to paste in is visible and selected. Now paste should copy everything in the level, including the walls.
Thanks so much, this ...

You can't copy/paste multiple levels. You have to do this for each level separately.
The easiest way is to make only one level visible before you select all on that level and copy it. Paste it on a level in the second project (make sure the elevation, height, and floor thickness are the same ...

Greetings everyone:
I'm using SH3D 7.5 in MX Linux, I'm trying to copy/merge a project into another one (project1 into project2), in project1 I've done select all on all levels , but when I paste into project2, the walls were not copied, what I'm missing? I've also noticed that it copied into grid 0 ...

Read this tread.
Preferably entirely.

Thanks so much for this tip.

I can't find very basic electric symbols for an electrical panel, since it's a very simple 2D design, thinking in making it in Blender or GIMP, is there any tutorial showing how to create a 2D design and group it in a library?

use Modify Walls -> Pattern and color of the top

H

Thanks for this tip, I don't see dotted wall, do I need to add additional pattern or just use a different pattern/color?

Is there a way to design a dotted wall? I'm thinking in doing a renovation, so I'd like to make part of existing wall dotted and new wall with normal line/wall. So in the 2D I can see the existing floor plan (with dotted wall) and future one (with full line). How can I do that?

Thanks you all for these tips.

My home has 3 fences surrounding it, is there a way to "connect the fences" like we connect the walls so when we move one point, the other parts move along with it? What if the part of the fences has wall, the same idea (connect fences with wall, so when you move one, move the other).

Rooms don't have to be rectangle. Just draw any shape, maybe disabling magnetism.

in its property, the angle is grayed out

What dialog box are you talking about?

Yes, that's it, disabling magnetism did it. Thanks.