help! how to paint a finished steel barn

My 36'X48' forest green barn was built 9 years ago. It was purchased as that finished, 40 year gauranteed metal. I hate the color and want to change it to match my new house. I don't know where to start. I've heard to just paint it, I've been told to prime it and then paint it, also been told to sand it all off, prime it and paint it, (not an option for me). IDK what to do. Also I want a good paint and finish. Something that does not get chalky or fade. Any ideas??

If you mean metal like R-Panel then it's a baked on enamel. You would die of old age before you sanded the paint off that building. I would start by cleaning the building with Krud Kutter Gloss Off and a power washer and then prime the building with a bonding primer such as Stix and then you could use the paint of your choice. I would recommend Sher-Kem enamel. As much building as you have either buy a cheap airless sprayer or rent one. It would be worth every penny.

(quoted from post at 18:28:27 08/19/14) If you mean metal like R-Panel then it's a baked on enamel. You would die of old age before you sanded the paint off that building. I would start by cleaning the building with Krud Kutter Gloss Off and a power washer and then prime the building with a bonding primer such as Stix and then you could use the paint of your choice. I would recommend Sher-Kem enamel. As much building as you have either buy a cheap airless sprayer or rent one. It would be worth every penny.

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That's exactly the type of knowledge I am looking for. Yes it IS baked on enamel, and I am already old, lol, so ya sanding it off its not an option. I really appreciate your input

Well, since you asked, and only since you asked... that is huge, and I personally would get very tired working that, just to change colors. I really think you will just uglify it, and get about 2/3 done and get sick and tired of it.
Just plant Colorado blue spruces in front of it and go on.

I don't know the "proper" way but on the side of our old pole building where I leaned some wheels up against to spray paint JD yellow there is an overspray mark on there that has stayed on for 20 + years I bet now.

Maybe get some graffiti painters to come out and do some street art on the side of it ? That seems to stay on everything well too.

that is actually a marvelous idea. If I wasn't so "traditional" I might actually do that.

Start by pressure washing...let dry...prime rusty screw heads with a spray can of oil based fast dry primer..you can paint topcoat right after you are done priming..primer dries in 5 min..for the topcoat use a good ext acrylic enamel waterbase..PPG pittech or equivalent..Sherwin w also makes a good ext acrylic waterbase...spray it on with a good airless sprayer (graco,titan,etc) and use a 513 oe 515 tip..about 2200 psi on sprayer...get ready to paint fast or it will run..stay about 1 foot away when spraying..don"t paint on a windy day..it waste too much paint no need to prime the whole building...as long as it is clean when you start. Also make sure there is no mildew on siding..if there is..use a 50/50 mix of bleach and water first,before you pressure wash(this is very important)wait 10-15 min then pressure wash.
As long as you take care of the rust(with oilbase primer)and the mildew you will be good for 10-15 years...I"ve painted many steel buildings(been painting 36 years in ohio) and never had one peel....also this topcoat resist fading...I painted one med green 20 years ago and it still looks good..you mmight have to give it 2 coats,depending on color change...and that"s it...hope this helped.
Keith