Ansible - Dynamic List Creation

I have a list, based on the index value need to generate a new list
Here is the sample

- set_fact: buildslen={{ builds | length }}
- debug: var=exactlen
- set_fact: upg_version_list2={{ upg_version_list2|default([]) + builds + [ item ] }}
  with_sequence: start={{ exactlen }} end={{ buildslen }}

The problem is the list not getting generated based on the indexes. Any suggestions to resolve this issue