Fixing gutter capacity issue around patio

Hello,
I have a 30 y/o single story brick and tile house in Perth currently rented out. The gutters (~80 lineal meters) are corroded and need to be replaced. Outside the ktichen there is a timber frame patio with polycarbonate roof sheeting put up by a previous owner. The patio shape is complex because it follows the roofline which has a number of changes in angle and on the other side follows the paving which also changes angle. The patio roof (about 25m2) slopes into standard house gutter and during heavy rains it overflows and on a couple of occasions has come down the interior wall and window in the living room. I am hoping for some ideas on the best way to fix this.

I got some quotes to replace the patio with a skillion type sloping away from the house with its own gutter system but it will be at least $30k due to the surface area, the wastage of this shape and the need for other works like new soakwells etc. Ideally the paving and adjacent landscaping would be redone so the patio could be made smaller and rectangular but that costs more money. I don't want to go down this path at the moment and would rather do just what's required to fix the gutter issue. Some of the rafter hangers (may not be the right term) bolted to the metal fascia are fairly corroded and probably need to be replaced soon too.

Below are the ideas I've had:
1) Replace gutter like for like with slotted gutter on most of house and unslotted in patio - probably going to overflow at times
2) As above but try upgrading downpipes in patio area
3) Replace gutter in patio area with a box gutter. A couple of companies have quoted this however the rafter ends match the shape of the existing gutter and would need to be notched to house the box gutter. I have some concerns this will weaken them. The notched section would still be above where rafter hanger bolts on so maybe OK.
4) Try to re-arrange the timber packers that give the PC sheets their fall to slope away from the house gutter and run straight off edge. This isn't ideal but a lot of this would fall into garden area so could be OK
5) As above but also try and fit new gutter system to outside of Patio. Not sure how it would attach but possibly could be clipped to the edge of the timber frame. Would be a bit ugly sticking out and require a new soakwell

The tenants also say in heavy rain one of the downpipe holes overflows. A contractor has said a soakwell has probably collapsed and they want to dig up the paving an put a polypropylene one in. This costs an extra $1500 and they won't redo the paving afterwards so I am not that keen. I am also doubtful just one could have collapsed as I would have expected for a house of this era the downpipes are all manifolded together going to a couple of concrete soakwells. It seems to only happen in heavy rain so one drain overflowing occasionally doesn't seem that bad. I don't think it backs up the downpipe.

Quotes for option 3 plus installing a new soakwell for one of the downpipes have ranged from $12.5 to $23k which seems like a lot.

Any ideas would be greatly appreciated.

 

I had similar concerns last year and ended up chatting with a local HVAC professional who explained a bunch of stuff I didn’t understand before. If you're near Carrollton, I recommend checking out https://emersonproservices.com/carrollton/ — they were super clear and really helped me figure out a plan without pushing unnecessary upgrades.