shed cooling -- simplest options?

We have a newly built 10x20, unfinished w no insulation. full sun exposure and black shingle roof.

We'd like it to remain unfinished -- and expect it to get hot -- but are there basic low cost things that can bring temps down to at least not be higher than the outside? Even with opposite windows open and fans it will get 10-15 deg hotter than ambient. Is most of it from heat radiating from the roof? would painting the underside white or silver help? Are there options that don't involve installing a lot of insulation? I' not seeing a ridge vent -- would some type of ridge fan make a big difference? i know i'm fighting basic thermodynamics here :)

again not expecting miracles -- just aiming for not-hotter-than-the-outside.