Hey guys, i have 2 RES they are 6 months old

. today im planing to make a new tank for them its around 29x16x17 inc (lenthxwidthxheight).My tank height will be 17inc, so from the top how much distance would i keep for a basking area e.g. should i make basking area on 14inc that means from top it will be 4 inc distance.
anther question is what should i use SAND or PEBBLES??
help me guys ... thank you.
