If your girls are only 5 weeks old, it is quite common for them to sleep on the floor. Some won't get the hang of it till they're much older, even 10 weeks or better. If you could, the addition of "mini-roosts_ at a lower level (12" or so high) for them to practice on might help. I had little 4" high roosts in the brooder, then 8-12" in the coop. Once they were comfortable roosting on these, they soon found their way to my main roosts, which are about 4" high. I took the mini roosts out when 13 of 15 were using the main roosts at night (my flock varied in ages, the oldest are 10 weeks older than the youngest). Once the mini-roost was gone, they all used the main roost. I have a ramp similar to yours that no one seems to use. I put back a 1' mini roost that some will use as a mid-way hopping point.