basic idea about how its done.
following general steps to make top down assembly from skeleton model
create component in assembly mode then select skeleton model
choose default options and click ok
skeleton model appears in assembly model tree right click and open it
capture the outline of assembly in skeleton model
save and close your skeleton
back to assembly again create another part this time select solid in subtype
choose default options here.
place the component wherever you like,it's not known at this stage as where component will be placed,it can be tweaked later
open this newly placed part from model tree
to copy geometry from skeleton part navigate insert>shared data>copy geometry
i have not published geometry from assembly so have to turn off this option
from reference tab browse to skeleton part ,you can use default options here
from reference tab browse to skeleton part select geometry whatever you need to make part
make part with copied geometry save and close
when you save the part,it appears in assembly,same way do it for other geometry.