I will assume you are asking about box stall design. A number of different materials and designs will work and to come up with the "best" design for one situation may not be the best design for another. Little research has been done to determine what is the "best" when it comes to floors, walls, doors, etc. What should be considered best is the stall that provides the highest level of safety for the horse and the people working in the stall with the horse, adequate ventilation, and comfort. There are pros and cons for almost any type of flooring you may use from dirt to concrete covered with mats. Having said all of the above, I will try to provide some guidelines and leave expense as a factor out of the guidelines. First of all, most box stalls are designed for a barn or stable with a starting point of 12 feet x 12 feet. There is some evidence that a horse is more comfortable and rests better in a rectangular stall, for example 10 feet x 14 feet or some other larger measurements that provide a rectangular shape. The horse appears to be able to orient itself easier in a rectangular stall. This would make sense since the horse itself is not a square shape. In an ideal situation, the stall is constructed in a barn with an indoor alley and on an outside wall so the stall could have two doors. One would be a solid dutch door that hinges and opens to the outside. Door two would be a sliding door that opens to the alley within the barn. Both doors' openings would measure 4 feet wide x 8 feet high. As for stall floors, most stalls are constructed with a clay base, and bedding is added to that. To help with drainage, "French drains" can be added to the stalls. This is done by basically digging a posthole in the center of the stall and two or more corners of the stall. These holes dug to a depth of three to four feet are filled with coarse gravel up to about a depth of four to eight inches of the top of the hole and then finished with the clay base that the rest of the surface of the stall is finished with. These "French drains" will allow urine to drain from the stall so you do not have as great of a problem with wet spots and removing wet clay when stalls are cleaned. Of course, mats are often used as stall flooring over clay or concrete or other stall flooring surfaces. These work well as long as the stalls have adequate bedding and wet bedding is removed daily along with manure. As for stall wall construction, hardwood is probably the best. Concrete or concrete block works very well if the stalls are lined with some type of wooden "kick board" to a height of about four feet. The minimum height of the stall walls should be eight to nine feet. Minimum ceiling height should be nine feet, but most recommendations if there is a ceiling is to go higher, 10 to 12 feet again for ventilation purposes. Most recommendations are not to have a ceiling. Regarding ventilation, a stall slot vent is recommended for warmer climates 20 inches above the floor 2 inches wide by seven feet in length especially if foals will be in the stalls. A stall window six feet high and four feet by four feet is recommended when a stall has an exterior wall. Of course, this should have a grate or some other type of protective covering to protect it from a horse breaking it. The only other thing to consider in stall construction would be traffic flow: that is, moving horses in and out to make it as efficient as possible, as well as traffic flow as pertains to cleaning the stalls with whatever equipment would be used.