Ramp or Platform
It is rare that a ramp or platform is the best solution for getting a cat down from at height, but, when it's appropriate, it is simple and effective, and it's surprisingly fun to watch it work. A ramp or platform is suitable only in those cases where the cat is very low, typically below 15 feet, and does not need to be secured. For example, if the cat is on a low limb or the roof of a one-story building, a ramp or platform may be the easiest way to get the cat to come down on its own. A ramp can also be used to help a cat come down from a higher limb to the roof of a building or from a second-floor roof to a first-floor roof, so it's possible in some situations to use a ramp to get a cat down from a higher point by breaking the task into smaller increments.
A ramp gives the cat a way to come down the way it prefers, which is head-first and under his own control, and this is especially appropriate for feral cats. If you can give the cat a ramp at an angle down that he can manage reasonably comfortably with secure footing, he will almost certainly take advantage of it. The ramp needs to be placed in a solid, secure position. If it wobbles when the cat steps on it, he will likely refuse to use it. The ramp does not need to lead the cat all the way to the ground. It can be placed on top of a step ladder, fence, or a vehicle or anything that gets him much closer to the ground while also making the angle down much easier for him to negotiate. He can usually jump to the ground from the bottom of the ramp. For skittish cats, you may need to leave the area and give him some quiet time to discover it and think about it, while other cats can easily be coaxed down to the owner or for food.
Long 2X4 or 2X3 wood boards are suitable for a ramp if they are covered with something the cat can grip with his claws such as carpet strips. You can also tack small strips of wood across the board at frequent intervals. Bare wood is too slippery for the cat, and he won’t use it unless the angle down is especially gentle. It’s a good idea to screw a large hook or drive a long nail underneath the top end to keep the ramp from sliding off the limb. You will usually need to join two boards end-to-end in order to make a ramp that is long enough to be useful. You can overlap two or three feet of the ends of the two boards and secure them tightly together with cam-buckle lashing straps. Long ramps can be difficult to maneuver without some help, and, like placing a ladder, you need to move it slowly and gently to avoid scaring the cat.
In place of a ramp, sometimes you may be able to make an intermediate platform that allows the cat to jump down to the ground. If the cat is fairly low but too high to jump down to the ground, you may be able to break that one big jump to the ground into two or three smaller jumps that are easier to manage. For example, you may be able to park a vehicle under the cat to let him jump down to the roof of the vehicle. Place a floor mat on the roof for secure footing and leave some food there to encourage him. You may also be able to make a platform using two step ladders with a board across the top or stack several large storage boxes up high. Get creative and use whatever you have readily available. The larger the landing surface, the better. You may need to entice more timid cats into jumping by placing some food in one corner of the platform.