Loft Conversion

I live in a terrace house with a plan as below
----------------------------------- ----------------------------------- party wall 9m meter lengths = / - / = / - / = / - / = / - / ------....------------------....---- party wall 9m meter lengths ------....------------------....----
/ is jiosts 8" by 2" 4.5m legths so the width is 4.5m in total from party wall to party wall
= roof with tiles on
- is wall through middle of house which goes to foundation single brick
..... where my and my neighbours jiost go through the party wall i.e his conversion and the one for his house and mine.
with limited ability to show drawings, below is where the tiled roof section is tyed together with 4" by 2" wood 4.5m lengths bolted together to form 9m lenth then bolted to the roof trusses
----------------------------------- party wall 9m lengths ='''''''''''''''''''''' -''''''''''''''''''''''''''''''''''''''='''''''''''''''''''''' -''''''''''''''''''''''''''''''''''''''='''''''''''''''''''''' -''''''''''''''''''''''''''''''''''''''='''''''''''''''''''''' -''''''''''''''''''''''''''''''''''''''------....------------------....--- party wall 9m lengths ------....------------------....---
would I be able to put four jiost into the party walls and tie these together with wood on jiost hangers to creat a grid like below and remove the above roof ties and replace with metal banding ?
----------------------------------- ----------------------------------- party wall 9m lengths = / / / - / / / = / / / - / / / = / / / - / / / = / / / - / / / ------....------------------....---- party wall 9m lengths ------....------------------....----
would you recomend putting the joists through the wall or putting them on heavey duty jiost hangers either by carving out the morter with a grinders and remortering in the jiost hangers or bolting them to the party walls with heavy duty wall bolts ?
the webbing would be made up of jiost hangers nailed to the main jiosts
and then boarding over the top with chip board.
I do not rearly want to start romoving tiles from the roof as not looking to go the hole hog and fully convert just want a good solid floor so no chance of damaging the plastering below.
what size wood would be best and creat a solid floor i.e webbing and jiosts ?
I appreciate that I should get a structual engineer to look over everything but rearly do not want the expence. I cannot get building regs inviolved as they will not touch it as I only want to use my new wooden fold away ladders that I fitted just a week ago hense after looking on here realised that not a good idea to just board over the 4"x2"s that are holding up the cealing below I have already notices some cracks from me walking through the loft that where not there before lucky I have a plastering friend that is sorting out allot of work for me at the moment anyway.
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