By far the most common tent in the 14th century are round pavilions. What's on the inside is a subject of debate. There are 4 types of construction I can think of off the top of my head. Hoop construction far and away looks the best and is easy to transport, but none of the big manufacturers make them, it would be custom. Rope tension tents have just a center pole and then use weather lines and guy lines to keep the walls up. Also very easy to transport and looks good when you've got the ropes set up well. Then you have the spoke wheel setup. Tons of wood and lots of stuff to transport but looks good when up. Perimeter polls can also be used, but now you've got even more wood to haul around and they look kinda funky.
I've personally put up hoops, and rope tension round tents, and they're easy. I own a square tent with perimeter polls, and I'd rather have a hoop or tension round than my square perimeter poll tent.
As far as size, most of the big tent manufacturers make each model in various sizes, so just pick the one with a foot print big enough for what you want to put in it, taking in to consideration whether or not the walls slope.
Some of the common tent makers are:
Panther PrimitivesMidwest TentTentsmithsI have personal experience with Panther and Tentsmiths, both are great quality.
Examples:
Hoop construction and center pole:
Rope Tension only with just a center pole:
Spoke Tent:
