Hi there people, I've got a question!

I've created this model in SolidWorks and I'm stuck on how to make a negative impression of it which then can be milled.

I've experimented with the Mold tools and used the 'Offset Surface' tool which does give me a negative impression of it, but im stuck on extruding on the offsetted feature so it has flat bottom, so I can go ahead and mill it. The original model would then be discarded.

I've attached the part, with the surface offset already applied to it,  to give you an idea of what I'm saying .

The process I might be on about may be a long-winded way, so if you have an idea on how to do it in a easier way, feel free to point out whatI could do alternatively.

Cheers in advance,

-Usman.

PS: Sorry if I've posted in the wrong section/wrong format as I'm quite new to these forums.