Creating a custom tmux session example. Thanks to HXcaine and default (https://stackoverflow.com/questions/5609192/how-to-set-up-tmux-so-that-it-starts-up-with-specified-windows-opened).

custom_tmux_session.sh

tmux new-session \; \
  send-keys 'tail -f /var/log/monitor.log' C-m \; \
  split-window -v -p 75 \; \
  split-window -h -p 30 \; \
  send-keys 'top' C-m \; \
  select-pane -t 1 \; \
  split-window -v \; \
  send-keys 'weechat' C-m \;