I have a pork loin and I want to do like an in door bbq pork how would I do that

Make a Chinese style BBQ marinade and sour roast it on your BBQ.
very successful and succulent.
http://m.allrecipes.com/recipe/232681/char-siu-chinese-bbq-pork

Then oven roast it; keep oven temp low, roast in covered pan; check meat temp OFTEN as noted above, take it out at 145 and tent with foil for at least 15-20 min before serving. Again the oven temp, amt. of liquid, and length of cooking time will be different if you want it served sliced or served as pulled pork. Either marinate it or use some type of spice rub as pork loin is so lean today; there is not much flavor

The loin is a very lean cut, so you can't treat it like a shoulder and cooking it low and slow for hours. You could coat it with a barbecue-style dry rub and roast it and serve it sliced with a barbecue sauce. You don't want to go much above a final internal temp of 145F, so take it out of the oven at 138F or so. Carry-over cooking will do the rest.

If you've got a few hours spare hours before cooking, consider brining the loin to help keep it moist.

It is so easy to do in slow cooker or crockpot; there are wonderful recipes on line; decide whether you want to end up with a pulled pork or an intact sliceable version in order to choose a recipe. My preference is a cider vinegar based cooking liquid and I never add barbecue sauce until I am ready to serve it. So very easy to do