I am new to this site and to timber framing in general. I have built a few small traditional stick frame structures and lots of remodels. I am planning to build small cabin as a guest house and just a fun project. My question is I want to have a loft at one end and I will have to clear span 15’. What size 4x8, 4x10 ect should I use for this. I have access to 3x12 which can handle the task but would like to keep the joist spacing as far apart as possible and to keep the beam thickness at short as possible. I’m looking for that sweet spot I guess. The loft will be roughly 15x20 and used for a bedroom. I want to put tongue and grove on top to be visible from below. I’ve looked for sites that help with calculating this but have had little luck. Looking for good advice not criticizing comments. Thanks for the help.