i get this when i build the mod

Go to raw\rumble and make sure it's in there.

now i got
ERROR: Couldn't find material 'bo2_mtl_t6_wpn_smg_mp5_camo2'
   failed loading material 'mc/bo2_mtl_t6_wpn_smg_mp5_camo2' for asset 'sp/bo2_mp5' found in source file '../zone_source/mod.csv'
ERROR: Couldn't find material 'bo2_mtl_t6_wpn_smg_mp5_camo1'
   failed loading material 'mc/bo2_mtl_t6_wpn_smg_mp5_camo2' for asset 'sp/bo2_mp5' found in source file '../zone_source/mod.csv'

You are missing the materials. Did you convert the materials in asset manager?
Or if this is a downloaded weapon you probably forgot to copy some of the folders into your raw folder.