You can finish the family and join it into the surrounding concrete. You can always edit the sketch, cut the sketch of an area, finish, create new extrusion and paste current view: Just remember that all areas will have the same offsets. You can add additional areas to the same extrusion. If you expect change then it could keep things tidy but if you can’t think of a good reason to do it, remember that constraints add overheads to performance: Alternatively, you can enter a 3D or section view and use shape handles or the align tool. Take note of the work plane that you are using to make sure you extrusion is hosted to the right level. Underside of slab is -250 and the pile cap is -300 offset from SSL. You can set a value from within the sketch if you know the offsets. You now need to think about setting the depth or verticality of your infill (extrusion). Link your extrusion to the Structural Material to control all of your extrusion materials from the type dialog: You could sketch over the exact required area and lock a line to the beam but that adds additional computational weight for a ‘just in case’ scenario: The advantage to doing this will be that changes to beam width won’t affect the extent of our extrusion. This will join with the beam and effectively become redundant. Note that I have sketched over the beam which does not require an infill. Sketch the area that requires the infill. In place families offer an appropriate solution for project specific geometry. Sometimes there will be too much variability in depths to easily manage slab types and offsets of each instance. A structural slab can be sketched in the areas required with offset and thickness to suit the conditions. The method used will be depended on initial workflow and ease of change management. This can be achieved using a selection of methods. In modelling terms, the ultimate goal is to plug the small gaps between structural elements. Notably, pile caps that have been lowered down to nib level below underside of slab. There are many situations where infills will be required to tidy up cast in situ concrete.