Yeah, fraction conversion to decimal works fine. 1/2 = .5 1/4 =.25 1/8 =.125.
Remembering most building is based on factors of two. To minimize wasting material stick to the notion that walls stretched out in a linear fashion should add up to a round number divisible by two, on the outside measured walls. 12 by 16...24 by 32 sort of thing, in feet.
It’s great to pencil things out on a sheet or two of graph paper. Draw it out, remember paper is cheaper than lumber. I spent hours doing this with an architect ruler when I couldn’t do anything else. Referencing how to books from a bygone era when people did build their own houses. I’m pretty sure that stuff can be found on line....