what's the china fir wood? is it fir wood?

no, it is not a kind of fir wood though it called china fir wood, its genus name is Cunninghamia honours, for its details, pls see the blow description in Wiki.

/wiki/Cunninghamia

how long it can keep well in outdside?

china fir wood has great ability in oursie, it can keep well for many years evening without any protect, so pls don't worry.

can you custom it by our requirement?

yes, we can , we can drawing as your requirment first then make sample for your final confirm