well if TD mean Tower Defence
for a clock,i got a .CAP somwhere on my HD ...
http://dl.dropbox.com/u/9050706/Cap%26a ... ck_sys.cap
or you could use a global var named timer with the value between each wave of ennemy.
Lets say 30 seconds, create a GVAR then enter 30 in the value.
+ System: Every 1000 milliseconds
-> System: Subtract 1 from global variable 'timer'
+ System: Is global variable 'timer' Less or equal 0
-> System: Set global variable 'timer' to 30
here is the cap for the timer
and for the shop,you will need some array and complicated stuff that i still dont understand