Creating a Rigid Frame family... don't know where to begin?

I am new to creating families in Revit. Our company just hasn't had to do much of it yet.

Now, I am given the task of creating a rigid frame for an existing building that we are renovating. I'm not sure if I should model the angles and plates that make up the frame, or just model a mass of some sort?
Also, the frame has a curve where it bends, and I'm not sure how to do that either. Any help is appreciated!
I have included a picture below

I would start with Generic Model Family. Also you could model-in-place inside your project with Generic Model if you keep in mind your work planes.
The ideal is about the same, but lets start with starting with new Family using Generic Model. Pick New Family, then pick Generic Model Template.
Should open with vertical and horizontal reference planes in the floor plan Ref. Level. This would be your rigid frame base view. Pick reference plane then offset the center horizontal line for the width of the frame flanges, adding new reference planes above and below this line. now repeat to offset the center reference line, to add new reference planes above and below for the width of frame web member. Now Change to Elevation Front View, this should set your work plane to Center (front/back).
Now pick from the create tab, Extrusion, now sketch in the outside profile elevation of your rigid frame. Start at the base Ref. level and other vertical reference line. the vertical reference line is the center (left/right), but we will use the reference line for the back of your frame. so sketch your outside elevation of your frame. chain your lines together, and use the fillet arc line tool from the draw box to get your curved line. make sure all lines are connected at ends and do not overlap. do not close or finish, now offset all lines to the inside, for thickness of flanges of frame, again make sure that all lines intersect and do not overlap. use the edit fillet tool or drag line ends to close, always one that is off a bit. now you can finish this Extrusion, by picking green check mark. If you get any warnings go back and fix. what the Extrusion command is looking for is a closed outline area. Now change to the Floor Ref. level view. Now drag or use the align tool to align your extrusion to the outside reference lines for flange widths. Pick 3d view to checkout your work, but you have not completed your frame family, we need to add the web. Now change back to Elevation Front view. From the create tab pick extrusion again. now using the pick lines tool from the draw box, pick the inside line of each line of your frame profile elevation, finish extrusion. Now go to the floor plan ref, level view. now align this web extrusion, to the reference lines for the web thickness you added in the first step. Go to 3d view to check out your work. You can also use the join geometry tool to join the web and flanges together. To add a material parameter to this family, pick family types in the properties tab. Now save this family to some location, and give it a name. If you have your project file open you can load this family into it using the load to project tab. To insert in your project model you will use the Component tab. You can place then mirror for other side of frame. I assume that this is a one time use family that does not need to be parametric for other conditions. To make parametric would require adding parameters to family with a few more steps.

Thanks for the reply. I will give it a go.
I don't imagine we will use this again, so I will not attempt to make it parametric!

You could mirror the other half of the frame inside of your family, and bring in as complete frame.
The generic model works as good starting point for most families, works great for rigid frames. But due to the nature of rigid frame you make run into problems with how it views in plan views
Next extra steps would be to learn about visibility settings to control how you want the frame to look in project plans and elevations.
Rigid frames columns due to slope may not view in plan as you want. The trick is to add model lines to base of your family that are visible only in the coarse view, and change the extrusions to be not be visible in coarse view. otherwise depending on were your plan view cut plane is you would see the frame flanges again above the base.
You can also add model lines for framing plan coarse views if you do not want to see the flange widths.Part of making a good family is testing and adding visibility settings that work with your view needs.

Good Luck