This is the list of parts and materials you will need for this project. They can be purchased at any electronic components stores and online retailers.
The Raspberry Pi
A USB keyboard (for setup only)
A 600 x 600 mm sheet of a 3 mm MDF
A 20 x 4 LCD (www.amazon.co.uk/2004-Characters-Display-Module-Blacklight/dp/B009GXWFSM)
0.1 inch female-to-female jumper wires
A small section of stripboard/prototyping board (www.maplin.co.uk/p/veroboard-copper-stripboard-100x160mm-a62rl)
Two 10 K multiple turn potentiometers (http://cpc.farnell.com/1/1/24068-trimmer-24-turn-10k-m64z103kb40-vishay-spectrol.html)
A row of 0.1 inch pin headers (http://cpc.farnell.com/starconn-connectors/phw-40-rv/0-1-pm-header-single-row-40-pms/dp/CN00870)
A row of 0.1 inch right-angled pin headers (http://cpc.farnell.com/starconn-connectors/phw-40-rd/0-1-pin-header-right-angle-40-pms/dp/CN00871)
A DC barrel jack (http://cpc.farnell.com/1/1/1498-2-1mm-dc-socket-psg01769-pro-signal.html)