Given that Plarium's Kabam forum is soon to be closed, I want to share this here for anyone who might find it useful.

Edal2007 said:

Well, i have second one lumber yard on lvl 21, other are on lvl 20, so don't know if i continue with lumbers or will upgrade sawmill?

What will give more resources on the final? Also need to look price of etchings for lumber yard and for sawmill, can upgrade two lumber yard for price of upgrade sawmill onlevel 6

Crowbar said:

This one seems easy.

If you have two level 21 lumberyards, and assuming the other three are level 20, your basic production is 2*500+2*340=1680. Getting another lumberyard to level 21 will add 500-340=160 lumber per hour for 120 etchings, which is 1.333 lumber/h per etching.

Adding another level to sawmill adds 5% to production, i.e., 0.05*1680 = 84 lumber per hour for 550 etchings, which is 0.153 lumber/h per etching.

Notice that I ignored sawmill and cannon bonuses which affect the former, but not the latter, i.e., with level 6 cannon and level 5 sawmill, this is 2.000 lumber/h per etching vs. 0.153 lumber/h per etching.

Btw, in my personal opinion, relying on production instead of raiding is a poor investment in every case.