Re: External threated timber cladding
Depending on what your purpose is will help decide the material you need.
Any of the pine, fir, spruce etc will need pressure treating to preserve the timber in any weathering position. The timber will also need surface treatment with protective oils etc to maintain the colour otherwise this will fade very quickly and lead to staining.
Cedar is a naturally oilly timber and is thus well preserved. It does require regular surface treatment to prevent drying and cracking, also to keep it looking well.
There is a plethora of buildings with untreated timber cladding that is just plain ugly within 6 months.
You also have options of vinyl cladding where maintainance is likely to be an issue or in particularily exposed site where weather has a greater effect on the timber.
There is little point getting a great deal on the price of the material if you will have to replace it in short time.