When I built my shop I did so with the intention of putting a full length 10' wide lean-to roof off the east side. Adding the ledger boards at the time of construction made it a lot easier
maybe a screened porch on the back.
If I made one renovation to my existing shop it would be to add a small open-sided carport off the garage door end, preferably with a contiguous slab floor. Some place shop-convenient where I could take boats when sanding to keep the dust out of the shop, wash boats when it is blazingly hot and sunny in the yard and dry tents and gear post trip when it is rainy. Taking wet sand or dirt spattered tents to hang dry in the basement means I have to vacuum up the detritus.
OK, maybe one wall on that carport where I could hang yard tools. And open rafters for storage. Maybe someday; it would have been much easier to build that carport at the same time, or at least like Alan have added the ledger boards during construction.
I like at least a few windows, in part for breeze and ventilation (and running an exhaust window fan during stinky tasks). But working with natural light is beneficial at times, so my main work surfaces, both seated and standing height benches, have a window. I am fortunate that the side of the shop with the two bench windows also provides a long view or who or what is coming down the driveway.
I think heating depends on the temperature extremes where you live. Hereabout the winter lows only occasionally see the single digits and summertime highs frequently top 100F. The concrete slab floor in the shop functions nicely as passive heating and cooling.
It is in the upper 80’s and humid outside right now, but my shop is at a comfortable 68. The slab floor is cool, almost cold still. By summer’s end the floor will have slowly warmed up and provide some passive heating in the winter months.
The shop was built over-insulated for this clime and even without running a heat source the shop rarely gets below 45F in the winter, so getting it up to a comfortable working temp is easy.
One downside to a slab floor is the humidity. We don’t have air conditioning in our home, but I use a window unit in the shop at times to drop the hygrometer.
Yeah, I have a hygrometer in the shop, and a barometer. And a min/max thermometer.
http://www.amazon.com/Min-Max-Thermometer-Button-Scientific/dp/B005QF35WY
Shop conditions are kinda fun to monitor.