Measuring Relative Levels (RL) and Floor Levels (FL) for landscape plan

I have a landscape plan with slopes and I’d like to measure :
FLs (floor levels) of paving and decking
RLs Top and bottom of walls
RLs Top and bottom of steps
Important spot levels

Is there a good tool or plugin?

THANKS!

I’m curious, is it RL or FL, you have one in the title and the other in the text.
I personally don’t know what either is.
It helps to avoid abbreviations when asking questions as the people who could answer your question may not understand what you are asking. This is an international forum with people from many disciplines. So someone with no experience in landscaping will probably be able to tell you how to do what you want to do because they understand the tools rather than the terminology.
But if they don’t understand the question…

Thanks for your comment! I have adjusted abbreviations…

I expect you could do that with the native Text tool.

Or maybe better, TIG’s Add Height From Datum
https://sketchucation.com/pluginstore?pln=heighttool_datum

Thanks Dave,
is there a way to set custom zero point in ‘Add Height From Datum’

Screenshot - 8_14_2020 , 9_00_33 PM