You'll set both the SRVHOST and LHOST as the IP Address assigned by DHCP, however port forwarding will need to be implemented through your Router / NAT Device in order to get external users to connect to you on the specific port. A more detailed example is, my WAN IP Address is 127.0.0.1 (Don't hack me guys...), I'm behind a router, DHCP has given me 192.168.1.100 in msfconsole I'll go:
set SRVHOST 192.168.1.100
set LHOST 192.168.1.100
set URIPATH /
And get the output as :
[*]Using URL : hxxp://192.168.1.100:8080/
After logging into your router, designate port 8080 on your specific IP Address to be allowed to be forwarded, the address you'll be sending people to would be your WAN IP : Port Number of The Server. Be sure you have written permission if your plotting an attack outside of your network - it's illegal if you don't.