The best plate material to use in a dry climate like Colorado is a 2x4 or 2x6 Treated LSL (Laminated Strand Lumber). Because LSL's are manmade, they are the least likely to move and most likely to stay straight. They also need to be treated because they come in contact with the concrete.
The second-best material to use in a dry aired climate are 2x4 or 2x6 Treated (KDAT-Kiln Dried After Treat). KDAT stays straighter because it's been dried which takes a lot of the moisture out and makes them lighter. Again, the plate material should be treated because it comes in contact with the concrete.
We do not recommend using green treated 2x4 or 2x6's. They just don't perform well in a dry climate.
Studs do not come in contact with the concrete and therefore do not need to be treated. In Colorado, we recommend the use of white fir for your 2x4 and 2x6 studs. White fir comes from the mid-west and works much better in Colorado. It is much less likely to warp and crack than the fir coming from other regions of the country. We also recommend using 2 and better 2x4 or 2x6 ~92 & 5/8 for an 8-foot ceiling and 104 & 5/8 for a 9-foot ceiling.
Ramset Loads and glue are needed to install the bottom plate.
3/4 OSB for flame block.
Nail Guns and pneumatic nails to put walls together before you put them up.
Foam to fill cavities.
County Line Lumber & Hardware carries all the material you need to finish your basement. Give us a call at 303-828-0102 if you have questions or want to place an order. You can also e-mail Joe at Joe@countylinelumber.com.
Picture: Treated LSL's (Laminated Strand Lumber).