Hi, Gerrit.
Thank you for you post. I see you're a practical man.
Let's be practical then.
The purpose of these symbols which include certain numbers is indication of altitude (relative and absolute) of different levels in a building (floors, landings etc) and its surrounding. They are given on section drawings as opposed to similar symbols with same function used on site and floor plans. I think that the sketchy image I posted above gives an idea how they look like and what they serve to.
For now I'm sure they're used by architects in Balkan Peninsula region. I cannot say more than this about their usage by professions and regions. What I can say is that I haven't had any design during my architectural studies done without them. They are...a part of documentation, tiny but necessary.
How can we make them in SketchUp now?
We can draw few lines (which resemble the symbol) accompanied with text (say +5,70 [a comma used here is a decimal separator unlike some other countries]). Saved as a component the same symbol can be used on different places on section drawings (done by 'Create Group from Slice' function + 'make faces' plugin). The text itself differs from altitude to altitude so we need to make every particular component unique in order to change it - manually. The height value can be given by applying one of those TIG's plugins.
Or, we can use the method suggested by Jean.
Or, we can invent something more elegant. But no matter how inventive and imaginative we are it's for sure that one part of entire work must be done manually. We don't do that when we use the command for ordinary dimensional work. We just select the 'Dimension' tool, pick our reference points and - voilร ! Later the entity info gives us possibility to change text position, font style, choose different endpoints and alike.
Move on to the next step: how to introduce more dimensionning options? Theoretically we can make some branches to the existing tool or we can make some new tool. A quick review of SU tools shows us that SU uses 'one tool - one command' principle. What I mean by this is that if you choose 'Push/Pull' tool for instance, you won't see any other sub-command. The other thing is that you're able to repeat the same pushing to different faces by simple double clicking on them or you can make an array by using the 'Move' tool.
So I doubt that SU developers would place any new command inside an existing one.
What is left for me is to hope that one day I'll see a specific tool for getting an altitude value.