one part or many

Hey guys/girls I'm a noob with this.

I am asking a fundamental question for solidworks. I am trying tomake a model with many parts that are very similiar and amwondering what is the best approach.

For example, if I were to model a deck, all of the items are 2x4with only the length varying.

Should I model each part, or model one length (say standard 8') andinsert this part where needed and change the length within theassembly?

I tried the second approach with makes sence to me but when Ichange the length of one part, it changes all parts like a blockwould in CAD.

Again, I'm very new at this.SolidworksAssemblies