southernbelle,
I put pipes under my basement slab for the geo system, then the loop guy told me they were the wrong size, so he ran new pipes overhead. I wish I had contacted him earlier. So the answer is YES, invite the loop installer over before you pour the basement floor. You also might want to look into putting PEX in the basement floor for radiant heat. It doesn't cost much, and you only get one chance.

Hey Moe, I'm trying to think but nuthin's happening!