Structural engineer for A Garage storage loft

Im looking to make my garage loft area into storage for seasonal things and maybe hang 2 or 3 bikes. The rafter beams look like 2×6 or 2×8 spaced about 21-24 inches on center and to be sure if its safe and structurally sound im looking for a Structural engineer preferrably in the spring – kline area.

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Aside from the actually making the storage area, im not keen on whats safe, weight and structure wise.

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Does anyone have any good reccomendation and an average cost of these thing for a first time home owner? any info is much appreciated.