hi,
I've never experienced this before, cause I often use extrusion void to do what you've described.But I've notice the same than you did.
Using extrusion void, I can add dimensions when using reference planes in the in-place void.
Maybe a picture of what you've made will help us?

That would really help because this is jibberish to me....

Sorry to be confusing. This seemed like a straightforward way of placing a 'dap' (which as far as I can tell just means 'depression'). I've attached a series of images showing what I did. I'm most likely posting these incorrectly also, but here goes.

Here's the slab edge, which looks the way I intended.
SlabEdge_Section.jpg

I accomplished this by adding a void sweep to my structural slab.
VoidSweep_Section.jpg

Because I have this in many places, and wanted to be able to update it globally, I used a profile instead of sketching in place. Here's the profile.
ProfileFamily_Section.jpg

Here's the basic problem: I cannot dimension to the cut edge, even though it's modeled.
SlabEdge_Plan.jpg

Tried to add a reference plane in profile to give me something to grab to.
VoidSweep_Section2.jpg

I may just have to do it the long way and add model lines to the face of my slab and manually offset them from the edge, because I cannot even align to the edge of this void. That will totally defeat the purpose of using a profile in the first place; any change in depth or width will mean I have to go back and move the model line in every instance.

Thanks again for your attention,
-josh

(...wearing my admin hat...)

Welcome to the forum. I just want to give you some guidelines about posting images. When you are composing your message, please find the "Manage attachments" button; it is located in the lower portion of the page, under "Additional options". From there you can use "Add Files" > "Upload files" > "Done". This will insert your images as thumbnails that spread out only when people click on them.

Much better, thanks.

-josh

There's a slab edge tool in RST 2011 to do what you want, I guess it's the same in RAC 2011. Maybe you should update Revit?
2011 worth it.

I found a way: put a cut view on your edge, you should be able to select the corner of the top level slab, to sketch a vertical ref plane.
return to plan view, you have the plane and the slab edge to put your dimension.

It can be a little tricky, but it works. Use Annotate > Linear dimension (instead of Aligned), then hover the mouse over the endpoint on the top, where you want to begin dimensioning, type SE > click, then go to the other endpoint on the bottom and type SE > click again. Then move away the mouse to the right and click to locate the dimension. SE means Snap Endpoint.

Instead of using a void for you brick ledge, create a custom profile for your slab edge that also incorporates your brick ledge in it.
After you create your slab edge, just join it with the slab so it appears monolythic. You can dimension to it with no problem.

I sketched my slab to end where the stud is, then created my slab edge profile to insert at that point. Here are a few screen shots.