re: My builder asked me.....

I mean, technically speaking you cant decide if you'll "allow" a lien on your property provided that it's filed properly and within the appropriate time. The supplier is required to notify you he's providing materials to the builder if the builder is working for you and your bank. But I'd be careful about what you sign.

That being said, I'd demand lien waivers from your builder each month and a list of suppliers/ subs so you can make sure he's paying his bills. If you get a signed waiver and then someone files a lien, you can legally tell them to pound sand.

Edit: now that I'm thinking about it OP, the document they want you to sign is probably a notice of supplied materials. Lien law basically has a loophole that if a third party supplier provides material but doesn't tell the primary contractor within the timeframe, they forfeit their lien rights. I'm a little rusty on the time frame, I think it's within 90days of first delivery of materials.