What type of small boiler do you plan on building? HRT, Scotch, Sectional, Locomotive?
Here are two drawings I have, they are quick ones, but you should get the idea.
As far as the grates go, if you are to make your own, you can either have them run front to back, or side to side, both utilizing a roller system. In my drawing the grates run side to side and use a round rod that each grate is connected to that shakes all of them via one handle, I will draw it another day to get into more detail. Or you can split them up and have two handles, one for operating the front half, and one for operating the back half. Hope this helps.