I have a full wave loop in the attic. It is roughly 12' x 6' with one of the long sides near the apex of the attic along the ridge line and hanging at a diagonal angle following the 6/12 pitch or the roof. It is fed on one of the bottom corners. It does surprisingly well although not as well as te outdoor loops I've had. It does better than the doublet that is four feet above the ridge line outside (probably because I did a lousy job with the doublet??). I rarely use it as it is there only should bad weather take out my other outdoor antennas. There is a lot of materials in my attic - attic fan, ducting, wiring, stored things, etc. I have made both local and DX contacts with it.
it was a fun project and is an out of sight out of mind project I just don't often think about although it is connected to my antenna switch.
Have fun.