You can line the inside of the shed walls with reflectix and insulation.
http://www.reflectixinc.com/basepage...iveInsulations
For heat you can set up a thermostat to an oil filled radiator.
http://www.amazon.com/gp/product/B000FT1XZW
For cooling you can buy a window vented air condition with a thermostat.
http://www.amazon.com/AMCOR-KF8000E-.../dp/B000P6L91I
Or a casement A/C for a small window.......
http://www.bestbuy.com/site/olspage....ci_sku=8381985
Without air conditioning, an exterior temp of 99 degrees will mean an interior temp of well over a hundred. The reflectix and the a/c can keep that temp around 82 or so.
I would also stay away from a metal shed. Building the shed in a shaded corner of the yard also helps.