I could see someone helping you build a house, under certain conditions. They can't bring any substances (nails, planks, etc). Rather you would have the ability to make a storage area in your own workshop. It may hold any sort of RS gold supply for construction around 100 of each (500 for nails). You would not be able to withdraw from this item, just deposit into it.

When players draw, rather than the items they get a magic tablet/stone/certificate which somehow counts for this sum of planks, nails, magical stone, bagged plants, etc.. It disappears when departing the house by any way, cannot be traded along with the actual items remain in the magical storage. No experience is gained from using this (or possibly a fraction, to make it marginally worthwhile). Basically, this is the only means for the OSRS buy gold individual helping you build to acquire supplies. They'd shed no cash, and gain little if any experience. They could not put in rooms, or eliminate items only you. All they could do is build using the magic storage.