Developer Help Needed Here

i need really help

i want to create :
android_device_tree
android_vendor_tree
android_kernel_tree

but i don't know from where i start or how !!
i want really to build CM12.1 ROM from source

so any one could help me on that please ??

my device is : lenovo s850
my stock rom is : KK 4.4.2
my kernel v is : 3.4.67
my MTK is : MT6582

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