How Do I see the legnth of a line as i draw it?

How Do I see the legnth of a line as I draw it?

I want it to always show the length even after its drawn

During any operation (making an edge or circle or rectangle etc) the current dimension info is displayed in the VCB which should be in the lower right hand of your SketchUp modeling window.

It should be said that looking at the dimensions displayed there is not the best way to obtain a given dimensions in your model, in fact depending on how display precision is set it can be pretty impossible. The correct method would be simply starting a line (or any other shape or tool) and then let go of the mouse and type in the length you desire. I very rarely look a the VCB, except when casually using the tape measure to check something.

If you want to see info on any existing entity , open the Entity Info window which displays relevant info on whatever is selected, including the length of a line or edge. You can change the length by retyping a dimension into that field in the entity info window, however it’s much easier to just type the length you want when first making the edge.

is this request still topical?
if so, you could create a new tag/layer for your measurings and group your object together with the sizing.
When you scale the object it will also update the measurings:

at moments you dont need the measurings and want a clean area to draw, simply turn off visibility for the measurings:

Why do you want to clutter the model space with dimensions as you are modeling?