Setting aside allowances for availability, cost, personal preference, family and ethnic tradition; a typical barn hay loft would contain some of the following:

Hay J
Smell of Livestock  J

The large door (sometimes on both ends) for introducing hay, straw and other material for storage in the loft.   When looking at my pics, you might notice that a lot of these doors are open and hanging down.  There is one definite reason for this.

At the very top of the hay loft, a track or rail was suspended.   From that track, a metal device with wheels (called a trolley) moved freely from one end of the barn to the other, pulled from the overhang above the door to the back of the barn with a large diameter "hay rope", draw by a team of horses and later a motorized tractor.
A set of four long steel "hooks if you will" were inserted into a clump of loose hay or group of hay bales on a "hayrack" or open wagon.   Also attached to a tripping mechanism on the hay hooks was a lighter rope, controlled by the person inserting the hooks.  This rope was both used to "trip" and dump the load of hay as well as manually retrieving the hooks, trolley and hay rope.

The team or tractor drew the hay up from the rack to the track above and adjusted carefully, the trolley would then change directions and travel towards the back of the barn.  A person stationed inside of the loft would direct the dumping of the load with a signal such as "pull", loud whistle or other shout of some kind.  The inside person or persons' job would be to distribute the load with either "hay forks" or by stacking the bales, sometimes with a smaller hand held version of the "hay hook".

Now, this is where good family relations come in.   The person managing the team or tractor was quite often an available a relative that perhaps was not able to perform the heavy manual labor of lifting the hay.   This person could have been a child or spouse of the "rack person".   Attention to the detail at hand was very important.  Haying is performed in the  heat of the summer when tolerance is low to advancing to far and pulling the trolley through the back side of the barn;   Swatting at flies when the "rack person" has reared back on the trip rope……. And pulling them from the rack to the ground;   not to mention reversing too fast and either locking the rope to the ground with a hoof or wheel OR  to not slow in a certain spot to keep the heavy "hay forks" from plunging to the hay rack in a tangled mess ….. or worse to injure an unaware "rack person".

Now back to the open "barn door".  There are two types, one of which was the cloth flap on rear of a pair of long handled underwear (when open being referred to as "your barn door is open"; and the huge wooden door that is now hanging down.
Let's talk about the latter of the two.  J

This door, a very heavy and large (common would be 12 feet wide and 10 feet tall), was constructed solidly with wood to provide for years of opening and closing, guard against a strong wind, and access to parcels of hay or straw.   It was opened and closed carefully with the same trolley and rope used for the parcel.   When the door was closed, the hay rope was pulled tight and coiled inside of the barn, awaiting the next year.   
As the years of "haying" and feeding livestock hay from a loft when by the wayside, the ropes rotted, allowing the barn door to open.   The rope never replaced, the door never closed again.
There were also hinged side by side doors for smaller areas.   The hinge attachment has failed over the years on some of those applications also and allowed a door to sag.
The hay rope itself was primarily constructed of twisted "hemp" or "sisal", imported from the arid, humid southern hemisphere countries.   During the second world war, sources for that product had diminished through the dominance of the Japanese in some of the countries the product was imported from.  For a period of a few years, the "hay rope" was made of a natural fiber (whether it was actually or not) referred to as cotton.   While it was a very soft and pliable rope compared to the hemp rope, it did not last as long and was not as strong.   I suppose that if a hay rope was used today, it would be made of polyethylene or similar man made product.  Some sections of the cotton rope (now 60 years old) can still be found hanging in barns.
Besides the rope, a loft would be central to the milking section as well as the livestock harboring on an adjacent side of the barn (see the page about barn construction and terms), with doors or openings large enough to "pitch" hay or bales through to the livestock.
It would require a "ships ladder" to traverse from ground level to the top of the hay or straw pile inside of the loft, often traveling up a shaft to the top.   I have even seen an ingenious person carrier in the form of a vertical conveyor type belt with pedestals to stand on, stretched over wooden pulleys and moved by hand with a rope.
A "swing" rope was always a must for the children to play and swing within the barn as the hay level decreased.
The "hay fork" with 4 to 6 sharp tines on a long handle was forbidden to be removed from the loft for other purposes.    For those who in later years used the small rectangular bale for storing hay, would usually have a "hay hook" or two in the loft also.  (see also pages on farm tools)