How to write a custom function in a model in ruby on rails?

i have User model class created with devise. i have role field(admin=0,user=1)in my model my db myhtml

<%if  current_user.active_admin? %>
                <%=  render 'layouts/admin' %>   
                <%else%>
                <%=  render 'layouts/user' %>
                <% end %>
            #User.rb
            def active_admin?
            #your logic here
            end

i want to login if i am a admin check role is 0 render to layouts/admin else i am a user check role is 1 render to layouts/user. how to write a code in model