Is there a way to multi-delete materials?

You should then have the bottom part of the box:-



Now for the lid.
Again, there a different ways to make that.
What I decided for this, was to first add a "Loop insert" around the outside of the box (you will see why in a moment).
Go into "Edge selection" click on "Loop insert".




Move your mouse cursor over one of the outside edges of the box. You will see an edge loop shown, it will move up/down as you move your cursor up/down on one of the edges. When it is where you want it to be, left click. [you could use the options in the "Loop insert" to enter a fixed length, but adding manually is ok for this]. The edge loop added is highlighted in red.



Change to "Polygon selection" and select the top polygons on the sides of the outside of the box.



In the "Visual tools" Select "Duplicate", in the popup options window, select "Break into one new object"

Here I have hidden the bottom of the box, so you can see the duplicated polygons.



In "Edge selection", select one of the top edges of those new polygons.
In the "Visual tools" select "Cap Hole"



That will add a top to the lid.



To add some thickness to the lid, I will again use "Shell". This time, because I want the thickness to move outward, I enter a value of 0.2



I then un-hide the bottom of the box. Which gives me the completed (basic) box



Just for cleanup, I hide the lid, select the edge loop I added earlier to the bottom of the box, and remove/delete it.



There are of course further steps if you want to add fillets or support loops(for smoothing). But will stop here for now.

Just ask if anything unclear.

NOTE: If all this is something you already know, please do not take offense. I am not sure as to what information/help you may/may not need.

Thanks Steve, that worked so much better.

I'm still in the beginning stage. I've been doing this for a couple years now, but never got serious about it.

I can see how this can help me communicate what I am doing with my other DIY project.
It would help me, design what I am working on. And help me to communicate with others my ideas.

I never used shell before. That took care of the problems that I was having with everything combinding.
I was so simple, it only took me a few minutes to make the box.

Hi 3dwizzard,

Looking good.

Happy I could point you in the right direction.