There are a few things you need to consider when doing a brew using an adjunct or unmalted grain. What adjunct (starch) or unmalted grain are you wanting to use? How much of the grain bill is this adjunct or unmalted grain?
Different grain or cereal straches gell at different temperatures and the starch has to be gelled to breakdown in the mash. Barley, wheat and oat starches gel in the range of mashing temperatures (126 - 155 F) so they are easily gelled and broken down by malt amylases during mashing. Starch adjuncts like corn, rice and sorgum require precooking to at least 170 F to gel the starch before adding to the mash. This precooking is done with about 5% ground barley malt for the purpose of at least thinning slightly the cooked starch as it gels. The enzymes of this malt are denatured in the heating but at least they start the break down of the starch and thin the cooker mash slightly. 5% to me as a home brewer is a hand full of my ground malt and it can be 2 row not necessarily 6 row. Both have plenty of enzymes to do the job.
If your grain bill calls for a large amount of adjunct or unmalted grain then you need to cook a large volume of water with your adjunct so it is not too thick, assuming you need to do a cooker mash step separate from you main mash. This large volume could increase the temperature of your main mash beyond you target saccarification temperatures when you add it in. This could be tricky. When I have made adjunct brews in 5 gallon batch sizes, I cook about 1 lb of rice starch in about 1 1/2 - 2 gallons of water and then add this to my main mash of the same volume sitting at protein rest (122 F). This seems to work well in bringing my mash up to about 145 F when they are mixed. When cooking my adjunct mash, I watch the temperature and make sure the adjunct starch (rice in my case) reaches it gelatinization temperature of 170 F for at least 15 minutes. You can tell because it becomes extremely thick. Oh yea, I start with precooked rice which helps.
As far as flaked grains you buy at the brew supply, these grains are flaked at supposely high enough temperatures to gel the starch in question. So flaked corn is suppose to have the corn starch gelled in the process so you can add it directly to your mash. However, I have found this to be variable with the various grains and processors. I have switched to gelling my own adjuncts.
Does this help??
Dr Malt