I need a heat/ac combo for a barn 8×8 with 10ft barn style ceiling 6 ft walls. Would a LG 12,000 BTU w/ heat 230v be a good choice?

Insulation on walls?
Insulation in attic space?
Kind of floor?
Doors insulated?
Average temperatures in your area?
Is this just for storage above freezing or is it to work in and maintain 65-70 degrees?

The unit you spelled out here will probably run away with no problem heating your future building but it never hurts to ask other questions.

8X8 is floor area? 64 square feet? 12,000 BTU is 1 ton and certainly overkill for a reasonable insulated room if it is 64 sq. ft. 1/2 ton will do about 250-300 sq. ft. room if insulated, i.e. a bedroom. I have a 5,000 BTU window unit in an uninsulated 120 ft. sq. shed and it is more than enough.

Its not insulated yet. Has electric ran already . And putting in a home window .

Its not insulated yet. Has electric ran already . And putting in a home window energy efficient . .
Also will have indoor outdoor carpet and if I can manage to insulate the whole barn I will .

Also will have indoor outdoor carpet and if I can manage to insulate the whole barn I will .
Its also not uncommon for 90-95 ° summer days and 15-20 winter nights. (Southern Indiana)

Its also not uncommon for 90-95 ° summer days and 15-20 winter nights. (Southern Indiana)

And it will be used for loft storage and a dog house . I have a dura seal doggy door for it as well lol