I recently have created my own stalls for my horses in sims 3. Unfortunately, they wont sleep in there, they try to go somewhere else to sleep. I was wondering if there is any way to get horses to sleep in the same spot they are standing in... please help, this is very frustrating.

Is it in a separate place or do you have it on your home lot?

What I did when I made my own stalls is 'mark as favorite sleeping spot.' I do not remember if you have to do it while they're sleep or not. If so, let them sleep (assuming all this is on your own lot), use MoveObjectsOn to move them there, and then select that option.
If it's a stall off the lot, they'll usually come home. I believe there is a mod to stop that (possibly by Nona. She made a lot of horse mods).
Horses can be very finicky.

When I make my own stalls, the only way I can get them to sleep without marking a favourite sleeping spot (which i avoid so they can sleep in pastures too) is by deleting the gate. That way, the horse won't try to exit the locked gate to sleep somewhere else. Sometimes they still wont sleep but i just teleport them around the sstall until they do...