If i use .5 mg of ativan (lorazepam) every night for insomnia, in time will i build up resistance to drug and require a higher dose to give the same effect?

Very possible: This is a well-known and common risk of anti-anxiety medications chemically called "benzodiazepines" (or "benzos"). It's the main reason they are not recommended for long-term use, usually defined as over 2 weeks. Of course, not everyone reacts the same: some people develop tolerance (they "build up resistance") even sooner, while some take much longer, or never do. But why risk it?