The important thing to remember when choosing rough sawn lumber is that it will need a significant amount of preparation before it can be used for building projects. This means you should consider your carpentry skills as well as your access to the proper tools before purchasing any rough sawn lumber. Think about what projects you want to complete before you choose the wood, as the types of projects will often decide which type of wood is best. Two general varieties of wood exist: hardwoods and softwoods. Hardwoods tend to be more durable and resistant to damage, but they also tend to be more expensive.
Softwoods are more susceptible to damage and will warp far more easily than hardwoods. This means as the wood dries, it is likely to curve or curl, so you will need to pay much closer attention to this type of rough sawn lumber during the curing process. Rough sawn pieces of wood are shipped green, which means they have not been kiln dried or naturally dried; you will have to do the drying process yourself, which means you will either need a kiln or a space to store the wood during natural drying. It is best to choose hardwood rough sawn lumber for these purposes.
Rough sawn lumber is usually sold in much larger pieces than finished lumber, since the pieces will need to be cut and planed. Think about how large of a piece of lumber you need for your project, and buy a piece of rough sawn lumber that is larger than what is needed. You will eventually plane down the piece and even cut it to get it straight and flat, so having extra material is more conducive to getting the proper shape and size.
In general, rough sawn lumber is less expensive than finished lumber because it has not gone through any of the processing that finished lumber has. This can be advantageous, but if the wood is not dried and shaped properly, you can end up losing money on the project. Be sure to find out what grade the wood has been given before you purchase it; lumber yards will often sort through the wood when it arrives on site and give each piece a certain grade according to its composition and overall condition. Consider the types of projects you intend to complete when choosing the grade of lumber you will buy.