Building a mold for casting resin

I'd like to try to create a top for a coffe table using resin but will need
to custom build the mold. The item would be one piece that's 48" long, 17"
wide and 5/16 " thick on top, with a lower portion that would fit down into
the table and would be 46" long, 15" wide and 5/8 " thick. I'd also like to
embed items in the tabletop, which is what made me think of using resin for
the project. I'd also like to put six small holes around the top for screws
to affix the top to the table. For a project of this size, what would be
the best material for creating the mold?

Matt Lupo
matt at lupo dot com

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G. M. Lupo a.k.a. matt at lupo dot com

Up on the hill, they think I'm okay
Or so they say...