I realize that Constructs and Summonings have been covered on multiple threads AND the basic answer is to make them NPC's. But I know there are a few of us that dream of playing a Binder-type character or a Summoner/Tinkerer of some sort, so I thought I would post my general rule of thumb for allowing players to do such things.
1. Summoning or Making Constructs is more or less the same thing. If you are making a form with ectoplasm, roll Lore as normal. If you are making a golem from natural material, use Craft.
2. Complexity determines the construct's power level. As Mark suggested, 1 point of refresh = 2 shifts. Therefore 4 refresh leads to a complexity of 8. If a PC is creating the construct, then the refresh cannot drop below 0 without some sort of stunt.
3. Complexity also determines the construct's skill level. So if the complexity is 8 for 4 refresh, for example, your construct will have 16 skill points. You can assign these points however you wish so long as it keeps with the rules of PC skill ladders. As always, skills not assigned are assumed to be 0.
4. Once the spirit/demon/AI enters the construct, it will try to defy you. Roll a Conviction VS Discipline with the construct getting +2. If you succeed, the construct gains an obediance aspect like "I Obey Hubert" for the remainder of its existance. A player could give the construct a Discipline of 0 to aid their success in this role, but that would leave them with a minion that doesn't think much for its self.
5. Constructs shut down at sunrise, either falling apart or melting to goo as is appropriate. Extending the duration adds shifts of comlexity that do not add to Refresh costs or Skill Points. Alternatively the player can simply renew the ritual with the same construct/AI combo every day. Mechanically it boils down to the same as recreating the construct except you have the obedience aspect to compel or tap.
And there you have it. So far I haven't had anyone be able to break this system, but maybe you can. Any ideas for improvements or points I forgot to mention?