Area Loads for Non-Rectangular Area

Should be fine to crates nodes at the vertices of each area, then trace the distributed load between those nodes. The nodes must be in the same plane as the framing elements that they are tributary to.

In RISA-3D, area loads are either triangular or quadrilateral. So, you'd have to break a larger area down into Triangular and Quadrilateral areas. This is because the program is a general FEM program and not necessarily geared towards building type structures.

Now, there are programs (RISAFloor, ETABS, RAMSteel) that are more geared toward "area loading" of a floor system. That's because these programs are very much geared towards commercial buildings.

Thanks for the responses.
I put a dummy member on top of the walls then I extended and trimmed them to produce a node at the corners. To me, that was easier than finding the x value of this node and the y value of that node...There's probably an easier way, but it didn't take too long.

Any floor plate will naturally be broken up into rectangular/triangular sections (In your case, all rectangles), unless it's curved, which is a whole other problem (and even then, structurally, it's probably just triangles).

You don't need 1 area load for the whole floor, any sub-set of area loads that fill the whole area and land on members at each of their edges should be fine. Even weird shapes can be alight, but I try and help RISA out as I can when I'm modeling, I at least keep things nice and square where possible. I would probably draw your area loads between each girder line, and at each change in building perimeter, which likely corresponds to a girder line.

Modeling properly in RISA (or any FEM modler) is kind of an art, less an exact science.