Change UI on existing Android App

I have a fully working prototype of an app. It enables user to select an item from item list (example:bike, car, glass, milk). When user selects an item camera opens up, user takes a photo using phones camera app, then recorded image is opened in the app, and user can place a marker on photo to mark the item he selected from item list. So this is all done, here is what freelancer must do: App needs to be changed - first start screen must be added, where there are 3 items - measure one by one, measure user list and exit button. If user selects mark one by one workflow is similar as in case of prototype, user selects item from lists, camera opens user takes photo and places a marker. Based on marker position a couple of lines will be drawn, downsampled image with drawn lines and x,y coordinates is saved, and user gets prompted if he wants to continue marking items, or if he wants to finish. If he finishes - report is generated, containig downsampled images and x,y coordinates of marked points. Second menu item measure list should enable user to create his own list from a list of predefined items. for example user can add items glass, milk, car items to his user list. He is then prompted. when he selects, that he wants to measure this list app tells him mark glass, then he marks milk and finally car. When he finishes marking report is again generated.