I bought a Lemmer 1600 for exactly what your doing. Between the two farms I've put through at lot of paint in and it works very well for this. I also got the 4ft extention for the gun , the tip screws right on the end, with a swivle. So you can angle it and get a lot from the ground. We put the paint and everything on a little pick up or quad trailer and drove it around. Luckly with a long extension cord we were able to grab power at spots and had no issues. Last spring I did a bunch of buildings with red tin sheeting that was real fadded. I sprayed it first with an oil base primer then we went over twice with a latex top coat.

My Lemmer 1600  came with 25ft of hose but I bought another 25ft to make it 50feet.  As painting long buildings out side and stuff 25feet is too short. 

Home Depot sells the Titan ones I think which are probably fine too. I got mine from a Lemmer dealer as I had one close and he had all the attachements and parts right there.  Graco sells a whole line of these too so its what ever is close by I guess. If you are doing large amount of painting these things are a "must have" as far as I'm concerned. Only draw back is you have to clean it well and that takes time. When I clean it good to store it, it takes a good 1/2 hr. When we were painting the next day I just ran solvent (or water for latex) through the machine and left it till moring. On my machine is says when you put it away to store it have varsol in the pump an lines so that's what I do.