"You are big!"
Translation:Wewe ni mkubwa!
I'm not sure if it's standard kiswahili, but I've heard that you don't need teh word "ni" in predicate sentences like these. At least this is what is claimed in the FSI courses I've found online. But it wasn't accepted here.
If you use ninyi (plural you), then you should also use wakubwa. Mkubwa is only singular.