I am wishing to make a deer pole, It will be on my barn and it will need to support approx. 500-750 pounds.The deer are large here! No but the overkill is for safety and a trolley type of lift I will be attaching to this beam.This beam will be cantilevered from the end wall a full 8 foot.My truss spacing is 12 feet so my beam overall length will be 20 foot minimum. I will set the beam on the endwall truss and continue to the next interior truss to anchor.All I can find on this is deflection charts and I just want to support a deer safely. I am considering a H or I beam for strength and long life, I would want something corrosion resistant as it will be on the exterior and 20 feet up. I want it to last an not look rusty or otherwise bad.
Thank you for input!:D

What about booms used for loading hay? I don't know the weight they can carry. May want to contact a supply company that sells them. If you use a beam just keep it maintained to prevent rust.

Really do not see a question in your post, just a statement of what you have decided to do.
If your question is will a H or a W [I beams are not made anymore I think plus they where made of a higher grade of steel thus a lot more pricey] support the load the answer would be yes as long as the beam depth is over 6 inches. So far as corrosion, clean the mill scale off, prime, paint, and you will be fine.

I am wishing to make a deer pole, It will be on my barn and it will need to support approx. 500-750 pounds.The deer are large here! No but the overkill is for safety and a trolley type of lift I will be attaching to this beam.This beam will be cantilevered from the end wall a full 8 foot.My truss spacing is 12 feet so my beam overall length will be 20 foot minimum. I will set the beam on the endwall truss and continue to the next interior truss to anchor.All I can find on this is deflection charts and I just want to support a deer safely. I am considering a H or I beam for strength and long life, I would want something corrosion resistant as it will be on the exterior and 20 feet up. I want it to last an not look rusty or otherwise bad.
Thank you for input!:D
I am sorry for not being more clear. I do understand your advise and any other is opinions alone. I also know you are more experienced in this area than I and your opinions are all I am after.
To clarify I want to have a structure of some type capable of safely carrying 500 pounds at a cantilevered 8 feet .Of course I want it to be as small and light as possible to make installation easier but ample margin of safety. So the Question should have said "What type of material would it take to carry 500 pounds cantilevered from an end wall 8 feet and be somewhat long lasting."

Any steel W or H beam over 6" in depth will carry your load.
One limiting factor I think you might find would be the amount of upload, and down load force that can be excreted on your trusses

Excellent point and how can I determine that! Thank you !

Lol Now your getting into the carpenter trade which I know little about other than the fact wood hurts less when you bump your head into it.
Again it would be determined by how much a given load will defect a given size/material /span- truss member

I can attest to that also! Well the 6" is much more info than I had before Thanks so much for your help!

Your beam going to be coming out at the peak of roof or below it?
And how far below if below?

Your Steel beam should not rest on a timber truss! The bottom member of your timber truss is in tension and was designed at that load.. adding additional tension to it is not advisable! You need to strengthen it first! The internal members of the truss was design accordingly, place the extra load on the top (compression member) Steel density is well over 25kN/m2 (metric system) take this into account when you consider your design load. Also multiply that with a safety factor of 1.2 Dead load and 1.6 live load ( deer weight). Remember you masonry wall is limited to 7MPa Compression and 2MPa Bending. You'll probably be better off designing a separate portal for your crane. Remember thermal expansion and leave space for your portal to expand.