I need help in writing a code in Excel to run a macro that will
generate sequential numbers. The sequential numbers will start based on
a predefined list of already used numbers that cannot be used again (as
shown below ). The sequential number string will be determined by the
classification of the new data. As shown below if new data is BLDG, a
sequential number starting with BLDG05 will be assigned since BLDG04
was th last assigned sequential number.

Predefined list (Already Used #s)
BLDG01 HSKG01
BLDG02 HSKG02
BLDG03
BLDG04

For example,
Classification Sequential #
enter new data BLDG BLDG05
enter new data BLDG BLDG06
enter new data HSKG HSKG03
enter new data BLDG BLDG07

Anyone has any ideas or codes that can work? I'll surely appreciate it.