First things first: If you want the result to be an assembly of multiple parts - Then you should make them an assembly of separate parts instead of all in one part.
However: If you still want to make it all as one part the best way imho would be to:
Make the outer channel A shape in one sketch similar to your original and extrude but change type to mid plane.
Then make the inside of the channel sketch and cut extrude it.
Then make your brace sketch similar to your original and extrude the width that fits inside the channels but change type to mid plane.
I would recommend you take the info youv've learned so far, and start over.
Follow Nates advice, and start with the A frame only, doing a midplane extrude to create the feature.
Then create a second midplane sketch/extrude to create the crossmembers.
@TwinStar, Have you had a chance to got through the training videos on the Resources/Training page accessible from the Alibre web site.?
This is in the section for Alibre Design Training but would still benefit an Atom3D user.
View attachment 38920
Sketching - Alibre Design Training - Alibre
www.alibre.com
Now I'm here trying to determine the best way to draw the diagonal braces.
Jacob
I see no reason you can't create the diagonals the same way you did the crossmembers.