How is it possible to view the line thickness that you have set at the drawing surface? before you polot. I mean drawing and working with the actual line thickness that you set for the layer? and i do not mean using pline
Is that what you are after?
I'm guessing you mean lineweight, not thickness. Thickness is the "height" of an object in the Z axis.
Lineweight is the perceived "width" of an object, visible only when the lineweight toggle is turned on.
Then again, you can apply lineweights at plot time only using a plot style table in your pagesetup, and not use the AutoCAD lineweight feature at all.
Here are two lines, one with a thicker lineweight applied and the other set at 0.0
The LWT toggle is on.
In addition to what the others have mentioned, if you also want to see lineweights in your plots you will want to check the Scale Lineweights box in the basic (left) portion of the Plot dialog, and the Plot Object Lineweights in the expanded (right) portion of the same dialog.
All of the suggestions given so far should help you both in your model and in plots.