Well you are asking for help here so go one step further! Mappers here are generally very helpful and I'm sure they would be happy to hear someone else is trying to create a Let's Build.
On The Saferoom podcast we've talked a lot about our desire for more Let's Build maps, do you have an idea for the theme? In terms of resources sites like World of Level Design are a great place to learn the basic and complex methods in level creation.
Well I did try asking and I'm awaiting further replies. I'm trying to go for a scavenger themed gas up concept where players must go out through a series of obstacles to bring gas cans to the autosite, which can be defendable and upgradable. So far I figured a lot out on my own but I'm still running into some common issues.