When wanting a summon, or to create your own, there are a few steps you must take. First and foremost, you may join any scroll already made that you so choose as long as the creator of that scroll allows you to join. There is no limitation on you for when you may ask to join someone else's scroll.
If you wish to create your own scroll, there are a few requirements that you must meet in order to do so. The first requirement is that you as a member must have atleast 500 posts. You must also be atleast of Chuunin Rank in order to create your own summoning. You cannot have the same species that has already been created.
This is where you will learn the limitations of your summonings, and how you will be able to construct them. Each rank has what is considered, Summoning Ryo. This ryo does not affect the user's total. This is an understood set of ryo in which to build your creatures. The ryo amount is listed as such..
D Rank: 11,000 ryo
C Rank: 16,000 ryo
B Rank: 20,000 ryo
A Rank: 26,000 ryo
S Rank: 31,000 ryo
Now, when building your summons, you can only choose for them to have one rank jutsu that goes above their own. An example would be your D Rank Summon can only have one C Rank ability, your C Rank can only have one B, so on and so forth. However, your summon may have up to as many lower ranking jutsu that fit the price range of that particular rank that you desire.
Ex: Your S Rank price range is 31,000 ryo. If you so choose, you can have one S Rank jutsu (11,000, price may vary depending on power) 2 B rank jutsu (6000 each, price may vary) and 3 C Rank jutsu (2500 each, price may vary). Adding these together would give you a total of 30,500 ryo for that particular summon. With nothing costing 500 ryo, that ryo would simply disappear. However, you fit within the window, and your summon would be approved.
I know your asking. "Hey what about weapons?" This same ryo applies to buying a weapon for that particular rank, and making sure it stays within your budget. You will have to sacrifice jutsu/abilities of your summon, in order to fit them into your budget for that said rank to have a weapon. The same rule applies for the weapon as it does for the jutsu. A summon may only wield one weapon that is above its rank, the rest may only be at its rank or lower.
Now, what if you go over the price of your summon's particular price range? Well, simple. If you so choose, you may pull from your OWN ryo to help fund any 'small' overlap of your summoning ryo amount. This does not include using your own ryo to provide more techs for the summon. So, with that, you only have a 1000 ryo cushion for your summoning at each rank if you go over the original amount. Do not abuse this cushion, and that means trying to purposely squeeze in smaller techs. If you do so, you will be punished and stripped of certain techniques.
Overall this is a complex system, if you let it overwhelm you. Otherwise, if you keep within the means, youll be fine. Keep within the limit. There is only going to be allowed two scrolls per village, so discuss within your village, who gets to create the summons.
Final Note: No summons may use a cloning technique.