Now you're ready to start the real planning.  This is where everything should come together.  This where you solidify your ideas into plans and create actual drawings to scale that will enable you to create pretty accurate calculations of how much material you will need to buy.  If you can find a free program online for creating drawings that would be very helpful.  You can enter dimensions and programs like Autocad can deliver up calculations on the fly.  Autocad is most like too advanced of a program for anybody without training, but there are others that are very user friendly. After you've created a drawing with your chosen layout you'll know where you want to place your appliances, fixtures, cabinets, etc.  After you've drawn in all your elements and you have all the calculations for your dimensions, you should be able to pretty accurately calculate how much you need to buy. But if you buy just enough, almost every time you'll run out.  So you want to calculate for a small percentage of loss or frivolous use.  For example, if you're putting in a tile floor, then you will end up having to cut some tiles to fit in certain areas.  From this, sometimes you end up wasting part of the tile because it can't be used elsewhere.  So just make sure that when dealing with materials, not appliances and fixtures obviously, buy a little bit extra.  Because those extra trips to home depot add up to wasted time and money in gas, fast...