garage doors, as much as they are nice (doors that roll open in both directions) they can be a tad hard to actually seal for when you want to heat or cool.
--doors that swing open much like door going into nearly every house out there. there ok in small size, but "ughs" get to be a pain as they get larger / wider. from snow build up, to needing to keep area directly in front of each door empty of everything.
--standard garage doors that "roll up" much like every door a city owner might have on there garage to store a car/truck. just get them bigger (wider / taller) for tractors they seal good for heating/cooling, and possibility of garage door opener. plus many can be insulated or come already insulated. with various lock kits. that doesn't require you to go through a secondary small door, to unlock and open the door. the con, they tend to be a little more costlier vs other types of large doors. the other con to this style of door, is does it roll up into roll or does it roll up against and long the ceiling. if it goes up and across the ceiling, you loose valuable space to place lights. were for me, is wanted and needed many times.
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overall garage door height... can be a tough one...
preferably higher is better. when dealing with various tractors more so if you go with a cab or backhoe, not to mention the generic ROPS (roll over protection system) the upside down U shape thing that goes over driver, can get in the way with many folks. having to either fold them down, or look else were to park the tractors.
if you have any plans to buy a trailer / camper, those also can push the over all height of the door up higher.
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garage door width...
as much as it would be nice to have a large wide door that could take in 2 cars at one time. it can be rather heavy to open more so if springs get out of adjustment. let alone the initial "heave hoe" to open/close door to point were springs kick in. on other hand having 2 narrow of a door has cons as well. many times i park tractor in shed, but then need to drag out something else, make it a sprayer, push mower, push weed eater, portable table saw, generator, etc... being able to pull tractor directly into the center, and then having any were from 3 to 5 feet on each side of tractor as a walking path to exit the shed with doors fully open. can be extra nice. there is less "shuffle" of other crud to get the item i want out of the shed.
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cathedral ceiling vs standard generic trusses that run through the center of the ceiling...
as much as i hate the standard generic trusses, when it comes to lighting, they have proved to be very valuable to hang stuff from over the years. to also screwing shelves into, to keep them from tipping over on me. to shoving long stuff up on to (extension ladders, long 16 plus foot lumber, pipes, etc..) and abilty to run wiring / air hoses, etc... on, without having to tear everything off the side walls to run stuff like you would with a cathedral ceiling.
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placement of doors? having large door on at least one end. might be advised, and pending on how large the shed/barn/garage is, adding another large door if needed. i do prefer some extra standard house doors at different areas on shed, (one per side)
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lean to / loafing area. ((extend one or both sides of the roof)) out further, say 8 to 12 feet. it is nice to be able to park various tractor implements under a roof, without having to backup all strangely into a shed to park an implement, also tend to place a grill or like, maybe a few seats out there. along with nice place to stack some firewood.